Acute Promyelocytic Leukemia: Clinical Guidelines

List of Abbreviations

allo-HSCT – allogeneic hematopoietic stem cell transplantation (A16.05.001)

ALT – alanine aminotransferase

AST – aspartate aminotransferase

ATRA – tretinoin

ATO – arsenic trioxide

auto-HSCT – autologous hematopoietic stem cell transplantation (A16.05.001)

ESBL – extended-spectrum beta-lactamases

EFS – event-free survival

RFS – relapse-free survival

HDAC – high-dose cytarabine**

HIV – human immunodeficiency virus

WHO – World Health Organization

DIC – disseminated intravascular coagulation

DNA – deoxyribonucleic acid

GI – gastrointestinal tract

IA – invasive aspergillosis

IPT – immunophenotypic study

BM – bone marrow

CT – clinical trials

CT – computed tomography

LDH – lactate dehydrogenase

MDS — myelodysplastic syndrome

LDAC – low-dose cytarabine**

MRD – minimal residual disease

MP – mercaptopurine

MPD – myeloproliferative disease

MS – myeloid sarcoma

OS – overall survival

AL – acute leukemia

ALL – acute lymphoblastic leukemia

AML – acute myeloid leukemia

APL – acute promyelocytic leukemia

CR – complete remission

PCR – polymerase chain reaction

GVHD – graft-versus-host disease

DS – differentiation syndrome

LCE – level of confidence of evidence

US – ultrasound examination

GRS – grade of recommendation strength

CT – chemotherapy

CMV — cytomegalovirus

CNS – central nervous system

ECG – electrocardiography

EchoCG – echocardiography (A04.10.002)

FAB classification – French-American-British classification

FISH – fluorescence in situ hybridization

NCCN – National Comprehensive Cancer Network

** – vital and essential drugs

# – drug used outside of the indications, modes of administration, and doses contained in the medication's instructions for use (off-label)

Terms and Definitions

Acute promyelocytic leukemia (APL) is a unique subtype of acute myeloid leukemia (AML) characterized by the predominance of abnormal promyelocytes with a balanced translocation between chromosomes 15 and 17, generating the PML-RARa chimeric gene [1,2].

Assessment of treatment efficacy:

Complete remission (CR) – complete remission (CR) of acute promyelocytic leukemia is defined as a state of the hematopoietic tissue in which bone marrow aspirate shows ≤5% blast cells with normal maturation of all hematopoietic lineages, a peripheral blood neutrophil count of >1.0×10⁹/L, a platelet count of ≥100×10⁹/L, and the absence of extramedullary sites of leukemic involvement. These parameters must persist for ≥1 month. CR is determined without taking into account the detection of "minimal residual disease" (MRD) using molecular biological methods (quantitative PCR, fluorescent in situ hybridization (FISH)). Molecular genetic analysis of the bone marrow at the stage of cytological remission is not performed; the PML/RAR transcript may remain positive in patients at this treatment time point, which has no prognostic significance for APL and does not require treatment modification.

CR with incomplete hematologic recovery – complete remission with persistent neutropenia (<1×10⁹/L) or thrombocytopenia (<100×10⁹/L).

Minimal residual disease (MRD) – a population of tumor cells that cannot be detected by light microscopy, but is identified by more sensitive research methods capable of detecting 1 leukemic cell per 10⁴–10⁶ cells examined.

Molecular remission – complete clinical and hematological remission in which the initially detected PML-RARA chimeric transcript is no longer detectable by polymerase chain reaction with a method sensitivity of 10^-4.

Treatment failures:

Early death – death of patients during induction therapy.

Refractory form of acute promyelocytic leukemia can be diagnosed in the absence of complete remission after the completion of 1 induction course and 2 consolidation courses. According to most international and Russian experts, in patients with acute promyelocytic leukemia with a PML-RARA transcript proven by molecular cytogenetic studies using all-trans retinoic acid in combination with chemotherapy or arsenic trioxide**, refractory forms of acute promyelocytic leukemia do not exist. Refractory APL is observed in rare variants of APL involving the fusion of the retinoic acid receptor alpha (RARA) gene on chromosome 17q21 with other partner genes (other than the PML gene), such as ZBTB16 on chromosome 11q23 and STAT5B on chromosome 17q21, leading to the synthesis of ZBTB16-RARA and STAT5B/RARA chimeric products, respectively.

Relapse – more than 5% leukemic blasts in the bone marrow or any extramedullary involvement at least 1 month after the establishment of the first complete clinical and hematological remission.

Molecular relapse – detection of MRD by PCR in consecutive duplicate tests with an interval of at least 2 weeks, against the background of persisting clinical and hematological remission.

Neuroleukemia – any number of blast cells in the cytopreparation not explained by cerebrospinal fluid contamination with peripheral blood resulting from a traumatic lumbar puncture; and/or symptoms of cranial nerve involvement or other neurological symptoms associated with chloroma growth.

Remission induction – the first stage of APL treatment, the purpose of which is the fastest and most substantial reduction of tumor burden, elimination of clinical symptoms, normalization of hematological parameters, and achievement of complete remission (usually 1 course).

Remission consolidation – the second stage of acute promyelocytic leukemia therapy, which is the period of solidifying the achieved antitumor effect. The goal of consolidation therapy – to convert a complete hematological response into a molecular response (or remission). Usually, 3–4 cycles are administered. If a molecular response is not achieved, additional cycles of consolidation therapy may be prescribed.

Maintenance therapy aims to maintain the molecular response over a long period. This phase typically lasts from 1 to 2 years. Maintenance therapy is not required in all cases of APL: for instance, patients receiving tretinoin and arsenic trioxide-based therapy do not receive maintenance therapy.

Prophylaxis or – if necessary – treatment of neuroleukemia is a fundamental stage in the management of patients with high-risk acute promyelocytic leukemia. This stage spans all periods of protocol treatment – remission induction, consolidation, and maintenance therapy.

Bone marrow/hematopoietic cell transplantation (HSCT) – this term encompasses transplantation of hematopoietic stem cells from bone marrow, peripheral blood, and umbilical cord (placental) blood.

Complications unique to APL therapy:

Differentiation syndrome (DS), also known as retinoic acid syndrome – a life-threatening complication developing during the treatment of APL with all-trans retinoic acid (tretinoin**) and arsenic trioxide. DS is considered an inflammatory response-mediated syndrome manifesting as unexplained fever, leukocytosis, acute respiratory distress syndrome, pulmonary infiltrates on radiographs, hypoxemia, edema (hydrothorax and hydropericardium), weight gain, renal failure, and arterial hypotension [1,2].

Pseudotumor cerebri (Idiopathic intracranial hypertension) usually presents with headache, papilledema, 6th cranial (abducens) nerve palsy, visual field defects, and increased intracranial pressure in the absence of a space-occupying brain lesion or hydrocephalus. Pseudotumor cerebri in APL is associated with tretinoin administration, presumably via the same vitamin A toxicity mechanism that leads to increased cerebrospinal fluid production [3,4].

QT interval prolongation. Arsenic trioxide is associated with QT interval prolongation, which can lead to life-threatening arrhythmias (e.g., torsades de pointes) [5]. It is important to closely monitor electrolytes in patients receiving arsenic trioxide, maintaining potassium and magnesium values within the mid-normal ranges, and to be aware of other agents known to prolong the QT interval [6].

1. Brief information on the disease or condition

1.1 Definition of the disease or condition

APL is classified among acute myeloid leukemias (AML), which represent a heterogeneous group of hematologic malignancies arising from mutations in hematopoietic stem/progenitor cells, resulting in a block in differentiation and uncontrolled proliferation of undifferentiated malignant hematopoietic cells that crowd out normal ones.

APL is a well-defined nosological entity within AML with such characteristic clinical and laboratory features (typical morphology of malignant cells, severe hemorrhagic syndrome, hematoma-type bleeding, hyperactivated fibrinolysis, DIC syndrome, usually leukopenia) that the diagnosis can sometimes be established based solely on clinical manifestations. Nevertheless, it is this specific variant of AML that requires rigorous diagnostic verification using molecular genetic methods [7,8].

This is because APL is associated with one of the most fundamental discoveries in the biology of leukemias: the phenomenon of APL blast cell differentiation induced by retinoic acid derivatives — 13-cis-retinoic acid, all-trans-retinoic acid (tretinoin**, ATRA**), and 9-cis-retinoic acid. ATRA** became the first so-called targeted drug. The use of ATRA** revolutionized outcomes in APL therapy.

Following the introduction of ATRA**, the arsenal of effective pathogenetic treatments was expanded with arsenic trioxide^** (ATO^**), which is likely one of the most active biological agents in the treatment of APL. There is no longer any doubt that APL can be cured even without the use of cytostatic agents.

APL is a prime example of modern precision medicine. The introduction of the ATRA^**/ATO^** combination into medical practice has transformed APL from a fatal disease into a practically curable condition, even without chemotherapy. Ongoing pediatric studies based on the ATRA^**/ATO^** combination represent a breakthrough in the treatment of pediatric APL, symbolizing a treatment approach for malignancies without chemotherapy agents, which are characterized by both acute and long-term side effects [9].

1.2 Etiology and pathogenesis of the disease or condition (group of diseases or conditions)

The etiology of APL is unknown in the majority of cases. In recent years, an increasing number of cases of APL presenting as secondary leukemia associated with prior chemotherapy (CT) and radiation therapy have been described. Large multicenter studies indicate that secondary APL most commonly occurs no later than three years after the completion of CT for a primary malignancy involving topoisomerase II inhibitors (anthracyclines [ATC: L01DB anthracyclines and related substances], or mitoxantrone**, less commonly etoposide**). In 57% of patients, the primary tumor was breast cancer, followed by non-Hodgkin lymphomas, and much less frequently, Hodgkin lymphoma. The median time from completion of primary tumor therapy to the diagnosis of secondary APL is 24 months (ranging from 15 months to 8 years). As the aggressiveness of the chemotherapy regimen increases, the probability of developing secondary APL also increases, and the time interval from the completion of CT to the onset of acute leukemia may correspondingly decrease.

In 95% of cases, APL is characterized by a reciprocal translocation t(15;17)(q22;q12), which leads to the fusion of part of the PML gene located on chromosome 15 with the RARA gene on chromosome 17, forming the PML-RARA chimeric gene. In rare cases, the RARA gene may be fused with partner genes other than PML. At least 14 variant partner genes have been identified, most notably ZBTB16-RARA, followed by NPM-RARA, NuMA-RARA, STAT5B-RARA, PRKAR1A-RARA, BCOR-RARA, FIP1L1-RARA, OBFC2A-RARA, GTF2I-RARA, and more recently described IRF2BP2-RARA, FNDC3B-RARA, TBLR1-RARA, STAT3-RARA, and NUP98-RARA [10].

Cases involving these atypical RARA fusion partners often differ from classic APL by the absence of Auer rods in atypical promyelocytes upon morphological assessment; patients tend to be younger and may be less sensitive to differentiation therapy [11,12]. For instance, patients with ZBTB16-RARA and STAT5B-RARA chimeric oncogenes demonstrate in vitro and/or in vivo resistance to ATRA** and arsenic trioxide (ATO).

1.3 Epidemiology of the Disease or Condition

The epidemiology of APL in the pediatric population of the Russian Federation is insufficiently studied. Acute myeloid leukemia accounts for 20% of all acute leukemias in children and 6% of all pediatric tumors. New cases of APL occur at a rate of 0.7–1.2 per 100,000 per year [13,14].

Acute promyelocytic leukemia accounts for 5–10% of all pediatric AML cases [14]. Higher incidence rates have been reported in Italy, Spain, China, and Latin America, with the highest proportions of APL (up to 50% of all APL cases) recorded in Nicaragua and Argentina [15-16]. Incidence increases with age, peaking in the fourth decade, whereas APL is particularly rare in infants (the median age for pediatric cases is 9–12 years) [17,18].

According to data from the SEER population-based study between 1975 and 2008 in the United States, 1,397 patients under the age of 20 were registered, and the incidence rate was 0.06 per 100,000 population [19].

Within the framework of the APL-MRD-2018 study conducted by the Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology from 2019 to 2023, 777 patients with APL under the age of 18 were registered, with APL accounting for 26% (199 patients).

1.4 Features of Coding the Disease or Condition

C92.4 Acute promyelocytic leukemia

1.5 Classification of the disease or condition

List of APL variants and other myeloid neoplasms (WHO, 2016) [20,21]

The WHO classification (2016) categorizes all AMLs based on their cytogenetic and molecular genetic characteristics, and it is these features that define the clinicopathological groups. APL is included in the group

AML with recurrent genetic abnormalities

AML with t(8;21)(q22;q22); RUNX1-RUNX1T1

AML with inv(16)(p13.1q22) or t(16;16)(p13.1;q22); CBFB-MYH11

AML with t(15;17)(q22;q12); PML-RARA

AML with t(9;11)(p22;q23); MLLT3-MLL

AML with t(6;9)(p23;q34); DEK-NUP214

AML with inv(3)(q21q26.2) or t(3;3)(q21;q26.2); RPN1-EVI1

AML (megakaryoblastic) with t(1;22)(p13;q13); RBM15-MKL1

AML with BCR/ABL1*

AML with gene mutations*:

AML with mutated NPM1 gene*

AML with biallelic CEBPA gene mutation*

"AML with t(15;17)(q22;q12); PML-RARA"; RARA translocations with other partners are classified as distinct APL variants, for example, APL with t(11;17)(q23;q12); ZBTB16-RARA; APL with t(11;17)(q13;q12); NUMA1-RARA; APL with t(5;17)(q35;q12); NPM1-RARA; APL with STAT5B-RARA.

Prognostic factors

Patients with APL are stratified into risk groups based on complete blood count parameters at the time of disease manifestation:

• low-risk group: leukocyte count <10×10⁹/L

• high-risk group: leukocyte count >10×10⁹/L

Final risk group assignment is determined based on transcript analysis (minimal residual disease [MRD] status) after completing 2 consolidation cycles or prior to initiating maintenance therapy [22,24].

1.6 Clinical presentation of the disease or condition

Acute promyelocytic leukemia is a well-defined nosological entity with such characteristic clinical and laboratory features (typical morphology of malignant cells, severe hemorrhagic syndrome, hematoma-type bleeding, hyperactivated fibrinolysis, DIC syndrome, usually leukopenia) that the diagnosis can sometimes be established based solely on clinical manifestations. At the same time, there are APL cases that follow a less dramatic course: hemorrhagic manifestations are absent, and patients are monitored for leukopenia and moderate thrombocytopenia for several months. Manifestations of hemorrhagic syndrome (gingival bleeding, skin bruising, ecchymoses, petechiae, frequently epistaxis or gastrointestinal bleeding) are present in 90% of patients at diagnosis. Hepatosplenomegaly or lymphadenopathy is identified in less than 20% of patients [24].

Patients with APL, especially the hypergranular variant, may have a low leukocyte count and only rare leukemic cells in the peripheral blood. Although APL is generally not a rapidly proliferative acute leukemia, by the time patients develop symptoms, the situation has often become life-threatening due to the risk of catastrophic hemorrhage. How long APL is typically present in the preclinical phase is unknown, but at diagnosis, the bone marrow is often almost 100% replaced by malignant promyelocytes, leading to severe anemia, thrombocytopenia, and neutropenia. More importantly, this mass of malignant cells in the marrow provokes severe coagulopathy involving both disseminated intravascular thrombosis and primary fibrinolysis. The APL variant characterized by microgranular APL cells does not have any additional independent prognostic value, but tends to have a higher peripheral blast count and possibly more rapid proliferation. A leukocyte count >10,000/µL (>10x10⁹/L) at diagnosis identifies a high-risk APL subgroup, partly due to a higher rate of early mortality [25].

2. Diagnostics, medical indications and contraindications for diagnostic methods

Many recommended methods for diagnosing the disease and related conditions have a limited evidence base according to the scales for assessing the levels of reliability of evidence (LRE) and levels of concordance of recommendations (LCR) due to the lack of dedicated clinical studies. Despite this, they are necessary elements of patient evaluation to establish a diagnosis and select treatment tactics, as more effective and proven methods have not yet been developed.

Criteria for establishing the diagnosis/condition: APL is diagnosed regardless of the percentage of blast cells in the bone marrow aspirate or peripheral blood (PB) in the presence of the APL-pathognomonic chromosomal abnormality t(15;17)(q12;q11‒12) PML/RARα.

A summary table of examinations required for the diagnosis and verification of APL is presented in Appendix A3.1. Based on the clinical picture and the analysis of the results of the listed examinations, patients are stratified into molecular-genetic and clinical prognostic groups (Appendix G2).

2.1 Complaints and Anamnesis

The manifestation of clinical manifestations of APL is accompanied by complaints of weakness, fatigue due to anemia; the development of hemorrhagic syndrome of varying intensity due to thrombocytopenia and DIC, and infectious complications against the background of neutropenia. These manifestations may develop acutely or progressively increase.

In 40% of patients, hemorrhagic syndrome may present as cerebrovascular or pulmonary hemorrhage, which are caused by APL-associated coagulopathy involving both disseminated intravascular coagulation (DIC) and primary hyperfibrinolysis, and is either present at diagnosis or occurs shortly after the initiation of specific therapy [26]. This complication accounts for 10-20% of early hemorrhagic deaths and requires immediate emergency medical care [27,28]. Thrombotic complications are less common.

2.2 Physical Examination

Comments: during the physical examination of patients with APL, special attention should be paid to the severity of the hemorrhagic syndrome to take urgent measures for the prevention of cerebrovascular and/or pulmonary hemorrhage.

2.3 Laboratory Diagnostics

Comments: In 80% of patients, the manifestation of the disease is characterized by leukopenia (median leukocyte count is 1.8×10⁹/L). If a patient with acute leukemia presents with leukopenia <1×10⁹/L at diagnosis, especially in combination with hypofibrinogenemia, the promyelocytic variant of APL can be highly suspected. In 15-20% of patients, leukocytosis is detected at disease onset (median 83×10⁹/L) with an increase in leukocyte count to ≥150×10⁹/L. The overwhelming majority of patients (80-90%) have anemia, and in half of them, the hemoglobin concentration is <100 g/L. In 75% of patients, the platelet count decreases to ≤50×10⁹/L.

A complete blood count (CBC) (especially leukocyte and platelet counts) is performed daily in the first days of ATRA** therapy to assess the risk of differentiation syndrome (DS) (if there is a rapid increase in leukocyte counts, it is advisable to start DS prophylaxis even if there was no baseline leukocytosis; the platelet count should not be <30×10⁹/L, target level ≥50×10⁹/L), and then every 1-2 days until remission is confirmed. Differential count ‒ 2 times a week.

The differential leukocyte count (leukocyte formula) must be performed manually rather than on an automated analyzer. It is recommended to examine at least 200 leukocytes in a peripheral blood smear.

Comments: Platelet counts and routine coagulation parameters, prothrombin time, APTT, and thrombin time, as well as fibrinogen and fibrin degradation product levels, should be monitored at least once daily and, if necessary, more frequently until all clinical and laboratory signs of coagulopathy disappear.

Comments: obtaining a cytological bone marrow preparation by puncture (A11.05.002) is a mandatory routine diagnostic procedure. The procedure must be performed under combined inhalation anesthesia (B01.003.004.012)!!!!

Bone marrow smears are examined using May-Grünwald, Pappenheim, or Wright-Giemsa staining. It is recommended to examine at least 500 nucleated cells in the bone marrow smear.

To establish a diagnosis of APL in a peripheral blood or bone marrow smear, the presence of 20% or more blast cells is required. In APL with t(15;17), t(8;21), inv(16) or t(16;16) and in some cases of acute erythroid leukemia, the proportion of blast cells may be less than 20%. According to the 2016 WHO classification, the percentage of blast cells is calculated regardless of the erythroid lineage proportion.

In most cases, the diagnosis can be suspected upon morphological evaluation of leukemic cells. Blast cells in APL in most patients are primarily characterized by significant nuclear polymorphism and the presence of large purple-brown granules densely filling the cytoplasm, and a large number of Auer rods (classic hypergranular variant of APL) [45]. In 15–20% of patients, only a few small granules are detected in the cytoplasm of tumor cells or they are not detected at all, while all other signs (clinical, cytochemical, cytogenetic) of APL are present.

A classic feature of APL tumor cells is a very pronounced cytochemical reaction for myeloperoxidase (MPO) and lipids, detected using Sudan Black B (SBB) and chloroacetate esterase.

Performing a cytochemical examination of a bone marrow smear preparation (A08.05.012) is necessary even if a high blast cell count is detected in the peripheral blood. This is because in some cases cytochemical reactions may yield different results in peripheral blood and bone marrow cells, which can lead to an erroneous diagnosis. The diagnosis is based on the results of the examination obtained on bone marrow cells. Reactions for myeloperoxidase (MPO) or Sudan Black, nonspecific esterase (alpha-naphthyl acetate esterase, inhibited or not by sodium fluoride), and PAS (Periodic Acid Schiff) are used. A classic feature of APL tumor cells is a very pronounced cytochemical reaction for myeloperoxidase (MPO) and lipids, detected using Sudan Black B (SBB) and chloroacetate esterase.

Based on the cytochemical examination of bone marrow blast cells (Cytochemical examination of bone marrow smear preparation, A08.05.012), about 90% of APL cases can be diagnosed; in the absence of MPO and nonspecific esterase activity, immunophenotyping by flow cytometry is required.

Comments: Immunophenotyping (IPT) is always performed on bone marrow cells, even if a high blast cell count is detected in the peripheral blood. Determining the percentage of blast cells by flow cytometry at initial diagnosis does not replace morphological counting, as the results of these two tests may not match [46].

To confirm the myeloid lineage of tumor cells, it is necessary to evaluate the expression of myeloid antigens. MPO is a lineage-specific marker of the myeloid line, a lysosomal enzyme of granulocytes. Less specific myeloid-associated antigens include CD11b, CD11c, CD13, CD15, CD16, CD33, CD64, CD65, CD66b, lysozyme, and others

Blast cells are considered positive for the expression of a membrane antigen if it is detected on 20% or more of the blast cells (cutoff value). For cytoplasmic markers (such as cytoplasmic CD3, MPO, lysozyme, nuclear TdT, and others), a lower cutoff of 10% is used.

IPT using multicolor flow cytometry can increase the accuracy of morphological studies in APL, but it is not a key diagnostic method. As a rule, PML/RARA-positive blast cells have an immunophenotype similar to normal promyelocytes (CD34‒/+ heterogeneous, CD117‒/+ dim, HLA-DR‒/+ dim, CD13+/++, CD11b‒). Nevertheless, unlike normal promyelocytes, PML/RARA-positive promyelocytes have an extremely low level of CD15 (CD15‒/+ dim instead of CD15+++). Blast cells in the hypogranular (variant) form of APL (M3V) often co-express T-lineage markers, such as CD2, along with myeloid markers, such as CD13 and CD33.

Comments: all cases of APL diagnosed by morphological and cytochemical methods must be confirmed by PCR or FISH at the time of diagnosis, since in 5-10% of cases in the absence of classical t(15;17), the PML-RARA transcript is detected.

Rapid genetic confirmation of the diagnosis is extremely necessary for diagnosing APL. Since the efficacy of targeted treatment based on retinoids and/or arsenic derivatives strictly depends on the presence of the PML/RARA chimeric gene, genetic confirmation of the diagnosis is mandatory in all cases. In 1977, J.D. Rowley et al. proved that t(15;17)(q22;q12‒21) is detected in almost all cases of APL [8]. As a result of this translocation, the promyelocytic leukemia gene (PML gene) located on chromosome 15 is transferred to the long arm of chromosome 17 to the region containing the retinoic acid receptor alpha gene (this translocation is classified as reciprocal and balanced, meaning genetic material is not lost and is transferred from one chromosome to another. As a result of t(15;17), 2 abnormal fusion genes appear: PML/RARα on the derivative of chromosome 15 and RARα/PML on the derivative of chromosome 17.

Genetic confirmation of the diagnosis must be performed on blast cells obtained from bone marrow. The identification of APL-specific genetic aberrations in blast cells is carried out at the level of chromosome, DNA, RNA, and chimeric protein analysis using standard karyotyping, fluorescence in situ hybridization (FISH), reverse transcription polymerase chain reaction (RT-PCR), or anti-PML monoclonal antibodies. Accordingly, each method has its own advantages and disadvantages.

Karyotyping on G-banded metaphases (standard cytogenetics) obtained from bone marrow samples is performed using standard methods on direct 24- and 48-hour cultures. Despite high specificity, cytogenetic analysis is expensive, time-consuming, requires good-quality metaphases (up to 20% failure rate), and by definition fails to detect cases where PML/RARA results from a so-called cryptogenic rearrangement (false-negative result). This method allows for the detection of additional chromosomal rearrangements, but they have no significant prognostic value in APL. Cytogenetic analysis can be useful in cases of APL where synthesis of the PML/RARA chimeric protein does not occur. Standard cytogenetics can also help identify rare variants of APL, including those with t(11;17)(q23;q21), t(11;17)(q13;q21), and t(5;17)(q35;q21), leading to the synthesis of ZBTB16-RARA, NuMA-RARA, and NPM1-RARA chimeric products, respectively, as well as others described more recently.

FISH analysis for PML/RARα is performed using fluorescent probes. Although peripheral blood samples are suitable for testing in some cases (particularly when hyperleukocytosis is present at diagnosis), FISH analysis is best performed on bone marrow samples. This method is highly specific, has sufficient sensitivity, and is much cheaper and less labor-intensive than karyotyping. However, FISH provides no information on the isoform of the PML/RARA chimeric transcript, which is necessary for MRD molecular monitoring.

Nevertheless, FISH can be useful in the diagnosis of suspected APL cases in which the PML-RARA chimeric transcript is not detected. For example, FISH testing can reveal a rearrangement of the RARA gene, which may have a partner other than the PML gene.

RT-PCR analysis for PML-RARA is performed on RNA extracted from bone marrow cells, although the chimeric transcript is usually readily detectable in peripheral blood even in cases with leukopenia. RT-PCR analysis for detecting the PML-RARA chimeric product was developed and standardized within international cooperation. RT-PCR is the "gold standard" for confirming the diagnosis of APL. Importantly, in addition to high specificity and sensitivity, it determines the location of the PML breakpoint, thereby establishing a marker for subsequent MRD monitoring. However, a small amount of RNA (and consequently a false-negative result), contamination/artifacts (false-positive result), and a relatively long sample preparation period (about 2 days) are the main disadvantages of this method. Furthermore, it is highly desirable that the detection of chimeric transcripts and sample monitoring be carried out in reference laboratories with well-trained personnel and extensive experience. In clinics that lack the capability to perform cytogenetic testing, the diagnosis must be confirmed in a reference laboratory. Bone marrow or peripheral blood samples must be delivered to the laboratory before therapy is initiated.

Determining the molecular variant of APL (PML-RARA, ZBTB16-RARA, NuMA-RARA, NPM-RARA, STAT5B-RARA, etc.) can indicate whether tumor cells are sensitive to ATRA** and arsenic. APL variants with the ZBTB16-RARA and STAT5B-RARA oncogenes respond poorly to retinoid and arsenic therapy.

Comments: Since complete remission is currently achieved in virtually all patients with genetically proven PML/RARA APL, both with ATRA plus chemotherapy and ATRA plus ATO therapy. This fact should be taken into account when performing the 1st follow-up bone marrow (BM) puncture, which should be performed no earlier than the 30th day after completion of the chemotherapy course. Earlier analysis of BM aspirate may lead to a false count of the percentage of blast cells—tumoral cells continuing to differentiate, which will completely disappear from the BM within 7-10 days. Thus, the first follow-up BM puncture is performed on average on the 30th day (sometimes on days 40-50) of remission induction or upon final recovery of peripheral blood counts. This delayed differentiation of blast cells can lead to a false-positive MRD determined by any genetic methods. Thus, MRD assessment after induction is questionable, except for research purposes.

In contrast to the lack of clinical value of MRD performed at the end of induction, molecular analysis of bone marrow performed after the completion of consolidation is crucial for determining relapse risk [48,49]. Furthermore, if MRD positivity is detected (preferably by PCR), a confirmatory (repeat) bone marrow MRD test must be performed in 2 weeks, since early modification of therapy for MRD-positive patients yields better outcomes than treating a full-blown relapse. MRD monitoring should be performed in routine clinical practice for all patients.

Comments: mutations in the gene encoding FMS-like tyrosine kinase-3 (FLT3) are observed more frequently in APL than in other types of acute leukemia—in 30–40% of patients. However, although FLT3 mutations are associated with a higher leukocyte count at the time of APL diagnosis, they are not a prognostic factor and do not influence the choice of therapeutic strategy in the treatment of newly diagnosed APL; tyrosine kinase inhibitors are not used.

Comments: initial CNS involvement in APL is generally quite rare, but in the event of an APL relapse, about 10% of hematological relapses present with CNS involvement [4]. Because the majority of CNS relapses occur in patients with initial hyperleukocytosis, CNS relapse prophylaxis via intrathecal chemotherapy is administered only to high-risk patients and those who presented with CNS hemorrhage, in whom the risk of CNS relapse is significantly increased. The first lumbar puncture should be postponed until hemostatic parameters normalize

It is desirable to maintain a blood platelet count of 50×10⁹/L or higher before performing a lumbar puncture. If the platelet level cannot be raised to 30×10⁹/L or higher, in the absence of clinical signs of CNS involvement, the puncture may be withheld until the blood platelet count rises above 30×10⁹/L.

Comments: preservation of primary biological material is carried out in the form of DNA and/or RNA isolated from bone marrow cells or frozen cells. The material may subsequently be needed for molecular studies to determine risk groups, as well as within the framework of clinical trials (CT).

2.4 Instrumental Diagnostics

Comments: Brain CT in APL should be performed in all patients in the first days of diagnosis, as asymptomatic intracranial hemorrhages may occur. If headaches, meningismus, drowsiness, or lethargy appear during retinoid therapy, a brain CT must be performed, and a lumbar puncture is performed after the CT (if the platelet count permits).

2.5 Other Procedures

3. Treatment, including drug and non-drug therapies, diet therapy, and pain management

The prescription and use of medicinal products specified in the clinical guideline are aimed at providing the patient with clinically effective and safe medical care; therefore, their prescription and use in a specific clinical situation are determined in accordance with the instructions for use of specific medicinal products, implementing the precautions described in the instructions, and dose adjustments may also be made taking into account the patient's condition.

3.1. Main principles of APL treatment

Acute promyelocytic leukemia in children is a rare and currently potentially curable disease thanks to therapy based on targeted drugs and the minimization of chemotherapy exposure. The main cause of treatment failure in APL is fatal hemorrhagic complications at disease onset and possible infectious complications developing against the background of induced aplasia. Given the rarity of this pathology, the treatment of patients with APL should be carried out in specialized clinics under the methodological guidance of federal centers.

Comments: currently, there are 2 approaches to APL therapy in children: the first is based on ATRA^** + chemotherapy, and the second is based on ATRA^** + arsenic trioxide [9,60].

Comments: although there is a general consensus on the need for molecular genetic confirmation of the APL diagnosis, differentiating (targeted) and supportive therapy should be started before receiving the results of genetic tests. Any suspicion of APL must be taken into account: the presence of severe coagulopathy, hemorrhagic syndrome, leukopenia, or a characteristic morphological picture of blast cells in the patient. In all such cases, ATRA^** therapy should be started immediately and continued until the diagnosis is confirmed or refuted based on genetic testing.

Comments: in all patients, regardless of initial leukocytosis, the chemotherapy course must be started no later than the 3rd day from the start of ATRA^** therapy. In patients with a leukocyte count >10×10⁹/L, the course of antineoplastic drugs is started simultaneously with ATRA^**. The optimal day to start chemotherapy for patients with a leukocyte count <10×10⁹/L can be considered the 2nd day from the start of ATRA^**, since by this time the diagnosis of APL should already be confirmed and the probability of early retinoic acid syndrome is extremely low.

3.2. Initial actions for supportive therapy when APL diagnosis is suspected

Supportive therapy aimed at correcting hemostasis

Intracerebral hemorrhages, pulmonary and other bleeding are frequent life-threatening complications of APL due to severe coagulation disorders. These complications not only become the most frequent cause of death in the early stages of induction therapy, but often develop before the diagnosis of APL is established and therapy is initiated [61-64].

Comments: therapy should include fresh frozen plasma (FFP), cryoprecipitate and/or fibrinogen concentrate, and platelet transfusions to maintain a fibrinogen concentration level >1.0-1.5 g/L and a platelet count >50×10⁹/L. Maintain the platelet count above 100,000/μL for patients with CNS hemorrhage (until stabilization of the condition, normalization of coagulopathy, and at least 7 days from the bleeding event).

Monitoring of these parameters (laboratory control of disseminated intravascular coagulation syndrome treatment, B03.005.002) should be performed at least once daily (more frequently if clinically indicated). Such therapy should be continued throughout the entire induction period until all clinical and laboratory signs of coagulopathy resolve. Attention should be paid to factors increasing the risk of fatal hemorrhages and bleeding. These factors include: active or already occurred bleeding, hypofibrinogenemia (<1.0 g/L), elevated levels of fibrin degradation products or D-dimers combined with prolonged prothrombin time or activated partial thromboplastin time, as well as hyperleukocytosis, presence of blast cells in the peripheral blood, high creatinine levels, and poor performance status. Central venous catheterization, lumbar punctures, and other invasive procedures (e.g., bronchoscopy) should be avoided prior to initiating therapy and during the remission induction period due to the high risk of hemorrhagic complications.

Catheterization of the subclavian and other central veins (A11.12.001) should be performed by experienced physicians only after correction of coagulation disorders. In addition, the procoagulant status in APL may not only increase the risk of hemorrhagic complications but also elevate the risk of thrombosis. The benefit of using sodium heparin^**, tranexamic acid^**, aminocaproic acid^**, other anticoagulants, or fibrinolysis inhibitors is controversial and unproven, and these drugs should not be used outside of clinical trials. There are also reports of eptacog alfa (activated)^** (blood coagulation factor VIIa) (ATC – B02BD08) being used in cases of severe, life-threatening bleeding [67,68].

3.3. Treatment of patients with newly diagnosed APL

Currently, there are 2 approaches to the treatment of APL: the "standard" approach – involving the simultaneous use of differentiating therapy (ATRA^**) and cytotoxic treatment including anthracyclines (ATC: L01DB anthracyclines and related substances) and cytarabine^**; and the "alternative" approach, involving only a combination of ATRA^** and arsenic trioxide (ATO) for low-risk patients, with the addition of anthracyclines to this combination during remission induction for high-risk patients.

3.3.1. Specific APL therapy in children with concurrent administration

ATRA^** + CT ("Standard" approach)

Comments: the earliest randomized trials on the combined use of ATRA^** and CT demonstrated clear advantages of this approach over standard CT [73].

A series of clinical trials conducted over the past two decades has helped optimize the administration regimen of ATRA^** and anthracyclines (ATC: L01DB anthracyclines and related substances). Thus, a randomized study by the European APL Group showed that simultaneous rather than sequential administration of ATRA^** and CT is the most effective [74].

It was the results of these studies that led to the combined regimen of ATRA^** and anthracycline-based CT (ATC: L01DB anthracyclines and related substances) becoming the standard of care for primary APL [72]. There are no strict unambiguous recommendations for selecting a specific CT regimen. Most researchers lean toward using the risk-adapted Spanish AIDA protocol, as it shows similar efficacy while having significantly lower toxicity profiles [75].

Based on the experience of the Russian Study Group for Acute Promyelocytic Leukemia in Adults, the use of the AIDA protocol in patients with newly diagnosed APL is equally effective: the three-year OS and DFS were 86.7% and 75.8%, respectively. The induction phase is complex and requires intensive supportive care, whereas the consolidation phases are significantly less toxic and can be administered on an outpatient basis.

Abandoning the standard approach should only be considered in exceptional cases where CT is contraindicated (e.g., severe organ failure, anticoagulant therapy (ATC – B01A Antithrombotic agents), patients older than 80 years), as well as in situations where alternative induction therapy options are dictated by socio-economic factors or clinical trials.

A study conducted by the Russian-Belarusian pediatric APL treatment group using the APL 1993/98 and APL 2003 protocols demonstrated good overall therapeutic efficacy (EFS and OS were 79±6% and 93±3%, respectively), despite a reduction in the total cumulative dose of daunorubicin^** to 405 mg/m² and the single dose of ATRA^** to 25 mg/m² [77].

Comments: Remission induction and subsequent consolidations are performed according to one of the following regimens*:[175]

1. ATRA^**, Cytarabine^**, Daunorubicin^**

Induction for low- and high-risk groups

ATRA^** 25 mg/m²/day in 10 mg capsules taken in two divided doses with meals. The dose is rounded upward. The drug is administered immediately upon suspicion of APL until complete remission is achieved, but for no more than 45 days

Cytarabine^** 100 mg/m² as a 1-hour infusion every 12 hours from day 4 after ATRA^** initiation through day 10, for a total of 14 doses

Daunorubicin^** 60 mg/m²/day IV as a 30-minute infusion from day 4 to day 6, for a total of 3 doses.

Consolidation 1 for low- and high-risk groups

Cytarabine^** 100 mg/m² IV as a 1-hour infusion every 12 hours on days 1–7, for a total of 14 doses

Daunorubicin^** 45 mg/m² IV as a 30-minute infusion once daily on days 1 to 3, for a total of 3 doses

Consolidation 2 (intensification) for low- and high-risk groups

ATRA^** 25 mg/m²/day orally in 10 mg capsules in 2 divided doses for 14 days.

Cytarabine^** 1000 mg/m² IV as a 2-hour infusion every 12 hours on days 1–4, for a total of 8 doses

Daunorubicin^** 30 mg/m² IV as a 30-minute infusion once daily on days 1 to 3, for a total of 3 doses

Upon completion of the intensive phase of the protocol, recovery of blood counts, and a bone marrow aspiration, maintenance therapy (MT) is initiated. If minimal residual disease is detected in the bone marrow, the patient is reassigned to the very high-risk group. The total duration of the protocol is 24 months from the start of induction. Maintenance therapy is based on a combination of chemotherapy and ATRA^**

Maintenance therapy [14,79]

ATRA^** – 25 mg/m² per day for 15 days (starting from the third month of maintenance therapy) every 3 months during the first year. In total, 3 two-week courses of ATRA are given during the maintenance therapy phase.

Mercaptopurine^** (INN Code: 004120) (MP) at a starting dose of 50 mg/m² orally in tablets daily on an empty stomach in the evening

Methotrexate^** (MTX) – 20 mg/m² in tablets once a week.

Drug doses are modified by 25–50% depending on blood leukocyte counts; the leukocyte count should be maintained at 2500–3000/µL

2. ATRA^**, Idarubicin^**/Mitoxantrone^**, Cytarabine^** [14,79]

Induction for low-risk group

ATRA^** 25 mg/m²/day, from day 1 to day 30

Idarubicin^** 12 mg/m², short infusion, days 3, 5, and 7

Induction for high-risk group

ATRA^** 25 mg/m²/day, from day 1 to day 30

Idarubicin^** 12 mg/m², days 1, 3, and 5

Consolidation 1 for low- and high-risk groups

ATRA^** 25 mg/m²/day, from day 1 to day 14

Mitoxantrone^** 10 mg/m², short infusion, days 4 and 5

Cytarabine^** 1000 mg/m² IV as a 2-hour infusion every 12 hours on days 2–4, for a total of 6 doses

Consolidation 2 for low- and high-risk groups

ATRA^** 25 mg/m²/day, from day 1 to day 14

Idarubicin^** 5 mg/m², days 1, 3, and 5

Cytarabine^** 1000 mg/m² IV as a 2-hour infusion every 12 hours on days 2–4, for a total of 6 doses

Consolidation 3 for high-risk group

ATRA^** 25 mg/m²/day, from day 1 to day 14

Idarubicin^** 10 mg/m², Day 4

Cytarabine^** 1000 mg/m² IV as a 2-hour infusion every 12 hours on days 1–3, 6 doses in total

After the 2nd consolidation in low-risk patients and the 3rd consolidation in high-risk patients, a bone marrow puncture is performed to determine measurable residual disease (MRD) by PCR.

In case of MRD negativity, low-risk patients receive maintenance therapy, whereas MRD-positive patients receive Consolidation 3 for the high-risk group, followed by a repeat MRD assessment. If MRD remains positive, the patient receives treatment for refractory acute promyelocytic leukemia (APL); if MRD is negative, low-risk patients receive maintenance therapy.

For high-risk patients, a negative MRD after Consolidation 3 is the basis for initiating maintenance therapy. In case of positive MRD after Consolidation 3, the patient receives treatment for refractory APL.

CNS-directed therapy

Comments: all patients without initial CNS involvement receive a total of 3 endolumbar (e/l) administrations of Cytarabine^** at age-adjusted dosages (prophylaxis): the 1st administration – before consolidation, the 2nd administration before intensification, and the 3rd administration upon recovery from aplasia after intensification. Cranial irradiation is not performed.

Table 2. Cytarabine^** doses for intrathecal administration depending on age [174].

In case of initial CNS involvement (cell count >5/µl with blasts or epidural chloroma), e/l administrations of Cytarabine^** and Methotrexate^** at age-adjusted dosages are indicated; in case of poor tolerability, Dexamethasone^** – 2 mg should be added to the e/l administration. Punctures are performed once a week until cerebrospinal fluid is sanitized (at least 3 punctures), then – before chemotherapy courses, for a total of at least 5 e/l administrations. Chemotherapy drug doses for endolumbar administration [174]:

In case of initial neuroleukemia, the dose of Cytarabine^** for systemic therapy in the intensification course should be increased to 3 g/m² IV over 3 hours – 8 administrations in total.

3.3.2. Specific therapy for APL in children without chemotherapy based on ATRA** + ATO** ("Alternative" approach)

Comments: Over the past few years, a revolution has occurred in the treatment of APL related to the introduction of arsenic trioxide into first-line therapy for adult APL patients. This has led to the creation of chemotherapy-free APL treatment protocols. For the first time, Lo-Coco et al. (2013) in a randomized study compared the combination of ATRA^** + arsenic trioxide (ATO^**) versus ATRA^** + anthracyclines and related substances(ATC code: L01DB) in induction and consolidation in low-risk APL patients. Although the results in both randomization arms were excellent, a statistically significantly better event-free survival (EFS) and overall survival (OS) were observed in patients who received ATRA^** + ATO^** [80]. Following these results, pediatric hematologists also began creating treatment protocols for newly diagnosed APL consisting solely of ATRA and ATO for low-risk patients with the addition of low doses of anthracyclines (ATC:L01DBanthracyclines and related substances) into remission induction regimens for high-risk patients. In 2 completed multicenter studies in children with APL in China [84] and the USA [85], event-free survival rates for low-risk children were 97% and 98%, respectively, and for high-risk children, 95% and 96.4%, respectively. In both studies, anthracyclines (ATX:L01DBanthracyclines and related substances) were used only for the high-risk group during remission induction at a reduced cumulative dose (240 mg/m² calculated as daunorubicin^**). It is worth noting that in the AAML1331 study (COG, USA) [85], maintenance therapy was not included. This non-randomized study demonstrated that pediatric low-risk APL patients can be successfully and safely cured using ATRA^**/ATO^** similar to adult low-risk APL patients. The addition of only idarubicin^** to ATRA^**/ATO^** in remission induction at a reduced cumulative dose helps achieve excellent survival outcomes, while the omission of maintenance therapy allows all treatment to be completed within 9-10 months.

ATRA^**, ATO^**, Idarubicin^** [85]

Induction for low-risk group

ATRA^** 25 mg/m²/day in 10 mg capsules taken in two divided doses with meals. The dose is rounded upward. The drug is administered immediately upon suspicion of APL from days 1 to 28 until complete remission is achieved, but for no more than 45 days

ATO^** (arsenic trioxide) 0.15 mg/kg/day IV as a 2-hour infusion (the infusion can be extended to up to 4 hours if active vasomotor symptoms appear) from days 1 to 28 until complete remission is achieved, but for no more than 45 days

Dexamethasone^** 5 mg/m²/day orally or IV in 2 divided doses

Induction for high-risk group

ATRA^** 25 mg/m²/day in 10 mg capsules taken in two divided doses with meals. The dose is rounded upward. The drug is administered immediately upon suspicion of APL from days 1 to 28 until complete remission is achieved, but for no more than 45 days

ATO^** (arsenic trioxide) 0.15 mg/kg/day IV as a 2-hour infusion (the infusion can be extended to up to 4 hours if active vasomotor symptoms appear) from days 1 to 28 until complete remission is achieved, but for no more than 45 days

Idarubicin^** 12 mg/m² (0.4 mg/kg for children weighing less than 10 kg) intravenously as a 1-hour infusion on days 1, 3, and 5 (the drug may be replaced with Mitoxantrone^** at a dose of 15 mg/m² or Daunorubicin^** at a dose of 60 mg/m²)

Dexamethasone^** 5 mg/m²/day orally or IV in 2 divided doses

Consolidation 1, 2, 3 for low- and high-risk groups

Each consolidation cycle lasts for 42 days, with a 14-day break between them

ATRA^** 25 mg/m²/day in 10 mg capsules taken in two divided doses with meals. The dose is rounded upward. The drug is administered on days 1–14 and 29–42 of each consolidation cycle

ATO^** (arsenic trioxide) 0.15 mg/kg/day IV as a 2-hour infusion (the infusion can be extended to up to 4 hours if active vasomotor symptoms appear). The drug is administered on days 1–5, 8–12, 15–19, and 22–26 of each consolidation cycle.

On day 43 of the Consolidation 2 cycle, a BMA is performed to determine MRD using RQ-PCR:

If MRD is negative, the patient continues treatment with the Consolidation 3 cycle

If MRD is positive, a follow-up BMA with repeat MRD assessment is performed in 1–2 weeks. If the MRD in the follow-up BMA is negative, the patient continues treatment with the Consolidation 3 cycle. If the MRD value remains positive in the follow-up BMA, the patient is switched to the consolidation regimen for MRD-positive patients.

Consolidation for MRD-positive patients

ATRA^** 25 mg/m²/day in 10 mg capsules taken in two divided doses with meals. The dose is rounded upward. The drug is administered on days 1–14 and 29–42 of each consolidation cycle.

Cytarabine^** 1000 mg/m²/dose (for children with a body surface area <0.6 m², the Cytarabine^** dose is 33 mg/kg/dose) administered as an IV infusion over 1–3 hours every 12 hours on days 1–4 of consolidation (8 infusions in total).

Mitoxantrone^** 15 mg/m² (for children with a body surface area <0.6 m², the Mitoxantrone^** dose is 0.4 mg/kg/dose) administered intravenously as a 1-hour infusion once daily on days 3–6 of consolidation (4 infusions in total).

BMA for MRD assessment using RQ-PCR is performed on day 29 of the Consolidation cycle for MRD-positive patients

- If MRD is negative, the patient continues treatment with the Consolidation 3 cycle on day 57, provided blood counts have recovered (granulocytes ≥1,000/µL and platelets ≥100,000/µL).

- If MRD is positive after 1–2 weeks, a follow-up bone marrow puncture (BMP) is performed with repeated MRD testing. If MRD is negative on the follow-up BMP, the patient continues treatment with Consolidation cycle 3 on day 30 and upon recovery of blood counts (granulocytes ≥1,000/µL and platelets ≥100,000/µL). If MRD remains positive on the follow-up BMP, the patient is switched to allo-HSCT.

Consolidation 4

The 4th consolidation cycle is given on day 57 after the 3rd consolidation cycle and upon recovery of blood counts (granulocytes ≥1,000/µL and platelets ≥100,000/µL). Consolidation 4 lasts for 28 days.

ATRA^** 25 mg/m²/day in 10 mg capsules divided into two doses, taken with meals. The dose is rounded upward. The drug is given during days 1–14 of consolidation.

ATO^** (arsenic trioxide) 0.15 mg/kg/day IV as a 2-hour infusion (the infusion can be extended up to 4 hours if active vasomotor symptoms appear). The drug is administered on days 1–5, 8–12, 15–19, and 22–26 of consolidation.

CNS therapy

Diagnostic lumbar puncture (A11.23.001) should be postponed until coagulopathy symptoms are resolved.

• Since ATO^** (arsenic trioxide) crosses the blood-brain barrier, APL patients receiving ATO-based therapy^** without signs of CNS leukemia or CNS hemorrhage do not require CNS leukemia prophylaxis is not recommended [87-90].

GCP CGrade of Recommendation C (Level of Evidence ‒ 5)

Comments:

CNS leukemia is defined as:

- Any number of blasts in the cytospin specimen upon atraumatic (<100 Er) puncture

- Presence of blasts in the CSF during a traumatic puncture if the CSF L/Er ratio is 2 times higher than the peripheral blood L/Er ratio

- Clinical signs of CNS leukemia (such as facial nerve palsy or hypothalamic syndrome). Isolated retinal hemorrhage is not a sign of CNS leukemia.

- Patients with documented CNS bleeding and neurological symptoms fully attributable to CNS hemorrhage do not have CNS leukemia unless they meet one of the other criteria (CSF or mass lesion), but these patients meet the criteria for "CNS hemorrhage"

- Radiological evidence of a CNS mass lesion

CNS hemorrhage is defined as:

- Any radiological signs of hemorrhage into the brain parenchyma, spinal cord, or subarachnoid, subdural, or epidural space.

- Isolated retinal hemorrhage is not considered a CNS hemorrhage.

Indications for intrathecal therapy during induction

- CNS hemorrhage

- Patients with documented CNS hemorrhage will receive CNS leukemia prophylaxis, including triple intrathecal chemotherapy on day 29 of induction. (See the table below for age-based dosing).

- CNS leukemia

- Patients with CNS leukemia will receive twice-weekly triple intrathecal chemotherapy (with a minimum interval of 48 hours between procedures) until CSF clearance plus two additional administrations (minimum 4 and maximum 6 procedures). During induction, patients with CNS leukemia will also receive Leucovorin^** 10 mg/m² 24 hours after intrathecal MTX administration.

Indications for intrathecal therapy in consolidations 1, 2, 3

Intrathecal (triple) therapy is administered only to patients with CNS leukemia on days 15 and 43 of consolidation

Age-based intrathecal chemotherapy dosing table [192,186, 192,193]

Maintenance therapy

Comments: as demonstrated by the AAML 1331 study of the COG Pan-American group, the omission of maintenance therapy significantly shortened the total duration of APL therapy from more than 2 years to approximately 9 months while achieving high survival rates (2-year EFS 96.4%) among high-risk APL patients [85].

3.3.3. Management of adverse effects of ATRA** and ATO**

Prevention and treatment of differentiation syndrome

APL therapy using ATRA^** and ATO^** can lead to a severe, life-threatening complication – differentiation syndrome (DS).

Comments: administering dexamethasone^** at the slightest suspicion of DS is the standard approach to treating DS, although direct evidence that prophylactic glucocorticoid administration reduces syndrome-related mortality is lacking. Nevertheless, uncontrolled studies have shown that the percentage of fatal outcomes when DS develops against the background of prophylactic glucocorticoid administration is reduced.

The probability of tumor cell DS is higher in patients with initial leukocytosis (>5×10⁹/L) and renal impairment (creatinine >123 µmol/L).

Therefore, early initiation of chemotherapy combined with ATRA^** and prophylactic glucocorticoid administration is the standard approach to treatment in this life-threatening situation. In patients with a leukocyte count >10×10⁹/L, chemotherapy is usually initiated within a few hours after the first dose of ATRA^**. This is precisely what allows coagulopathy to be controlled while simultaneously reducing the risk of DS, the incidence of which is particularly high in these patients.

Management of hyperleukocytosis

Comments: Leukocytapheresis (hematopoietic cell cytoapheresis, A18.05.017) is not recommended as a routine procedure for APL patients due to the risk of fatal hemorrhagic complications and disseminated intravascular coagulation (DIC) syndrome. However, in cases of ineffective cytoreductive therapy in patients with hyperleukocytosis in life-threatening situations, leukocytapheresis (hematopoietic cell cytoapheresis, A18.05.017) may be used provided that the hemorrhagic syndrome is controlled to the maximum extent possible.

Monitoring side effects of arsenic trioxide^** (ATO^**) therapy

The use of arsenic trioxide can lead to QT interval prolongation and the development of complete atrioventricular block. QT interval prolongation can cause torsades de pointes ventricular tachycardia with a potential fatal outcome. The mechanism of ATO-induced cardiotoxicity mainly involves the accumulation of reactive oxygen species (ROS) and intracellular calcium 5,6. ATO can trigger cardiomyocyte injury via apoptosis, autophagy, and necrosis.

Cardiotoxicity manifests as QT interval prolongation on the ECG, cardiac arrhythmias, and decreased electrolyte levels (potassium and magnesium) in biochemical blood tests. If ECG changes appear, interrupt arsenic trioxide administration until all parameters normalize.

The most important additional side effects of arsenic trioxide are leukocytosis (initiate hydroxycarbamide if WBC >5,000/µL), ECG QT interval prolongation, and electrolyte depletion (potassium and magnesium) in blood biochemistry.

Comments: Certain medicinal products prolong the QT interval and may potentially exacerbate the effect of ATO on the QT interval. Caution should be exercised when co-administering any medications. A list of such medicinal products is provided in Appendix 2.

3.4 Treatment of relapsed and refractory forms of APL

According to various studies, ATO monotherapy in relapsed APL achieves a 2nd molecular remission in 70–90% of cases [47,48]. At the same time, transplant approaches in patients who achieve 2nd APL remission demonstrate superiority over ATO-containing regimens alone. For instance, a study by the European LeukemiaNet group showed a 3-year OS of 80% in patients after autologous HSCT in second molecular remission compared to 59% in patients without HSCT [49]. Although allo-HSCT is characterized by a lower probability of relapse post-transplant compared to auto-HSCT according to some studies, treatment-related mortality makes this approach less preferable in patients in second APL remission compared to auto-HSCT [50]. High efficacy of auto-HSCT should nevertheless be expected only in patients who have achieved a 2nd molecular remission.

Comments: although ATRA^** combined with chemotherapy can be used as salvage therapy, ATO-based regimens are currently considered the 1st line of treatment for relapsed APL.

Comments: autologous HSCT may only be performed if the harvested autograft is free of the molecular marker.

Comments: Despite the high efficacy of ATO in patients with APL, relapse after ATO therapy and resistance to ATO treatment remain a challenge. One approach to treating relapsed and refractory APL in such cases is the use of bortezomib^** in combination with ATO [101,102].

Comments: Venetoclax^** dosage table for children over 2 years of age by weight

3.5 Supportive and concomitant therapy

• All patients receiving therapy for APL are recommended to undergo supportive and accompanying therapy in accordance with relevant guidelines [7,104,107].

GDR CLE 5Grade of recommendation C (level of evidence – 5)

Comments: Isolation of children in single-bed laminar airflow rooms, infusion therapy, and the use of colony-stimulating factors as indicated are shown.

Comments: systemic antifungal therapy is continued until neutrophil counts rise above 0.5 × 10⁹/L.

Comments: The choice of initial therapy depends on the patient's performance status, screening results, prior infection history, as well as local epidemiological data and guidelines. Systemic antimicrobials in patients with APL are administered exclusively via intravenous infusion.

Comments: Glycopeptide antibiotics may additionally be prescribed depending on the clinical picture, local guidelines, and patient colonization. The prescription of carbapenems as first-line systemic antibacterial drugs is justified in patients with severe infections, abdominal or perirectal involvement, and sepsis. Modification of antimicrobial therapy is carried out based on clinical symptoms, instrumental findings, and microbiological test results. In a stable clinical condition and in the absence of infection foci, continuation of empirical antibacterial therapy for 48–72 hours is permissible, as fever is not the sole indicator of the severity of the infectious process.

Comments: Patients colonized with resistant bacteria require the administration of reserve-group drugs (in accordance with antibiotic susceptibility testing data).

Comments: When severe infectious complications and/or sepsis develop, antibacterial drugs are prescribed at maximum doses, preferably via prolonged infusions due to impaired clearance and fluid redistribution in the body. Reserve-group drugs include colistimethate sodium, polymyxin B^**, tigecycline^**, #ceftolozane+[tazobactam]^**, ceftazidime+[avibactam]^** (in some situations in combination with aztreonam^**) [126-128,130,143].

• Proactive antifungal therapy is recommended for all patients with APL if signs of invasive mycosis are detected during a full range of diagnostic examinations: chest computed tomography, bronchoscopy followed by microbiological examination of bronchoalveolar lavage fluid (in accordance with Appendix A3.4) [131, 156, 157].

LoE 5Grade of Recommendation C (Level of Evidence – 5).

• Fluconazole^** is not recommended for the treatment of candidemia in all APL patients with neutropenia and/or hemodynamic instability [157].

LoE 5Grade of Recommendation C (Level of Evidence – 5).

• Upon the development of invasive aspergillosis, immediate initiation of systemic antifungal therapy is recommended for all APL patients [157-163].

LEL 5Grade of Recommendation C (Level of Evidence – 5).

• Upon the development of invasive mucormycosis, immediate combination therapy including systemic antifungal drugs and surgical intervention is recommended for all APL patients [157, 164-166].

Level of Evidence 4Grade of Recommendation C (Level of Evidence – 4).

Comments: Any manifestation of hemorrhagic syndrome (petechial rash, especially on the oral mucosa, face, and anterior chest wall, any bleeding) and/or a body temperature above 37.5^°C, even in the absence of a clear infection focus, requires platelet concentrate transfusion even if the peripheral blood platelet count exceeds 20×10⁹/L. Similar indications apply for platelet concentrate transfusion when preparing a patient for invasive procedures.

For the first induction phase and for performing invasive manipulations (lumbar puncture, central venous catheterization), the platelet count must be at least 30×10⁹/L. During the period of hematopoietic aplasia following any polychemotherapy course, in the absence of bleeding and/or infections with febrile neutropenia–platelets should be maintained at a level of at least 15×10⁹/L. When infections with febrile neutropenia develop and when Amphotericin B** is used, platelets should be maintained at a level of at least 20×10⁹/L.

Severe mucosal bleeding, gastrointestinal bleeding, pulmonary hemorrhage, and cerebral hemorrhage are indications for platelet concentrate transfusion regardless of platelet counts.

Comments: Indications and volume of transfusion support are determined by coagulogram parameters and the clinical situation.

Fresh frozen plasma transfusions are performed only for major coagulogram abnormalities: fibrinogen less than 1 g/L, prothrombin index less than 50%, aPTT greater than 55 seconds.

4. Medical Rehabilitation and Sanatorium-Resort Treatment

Approach to rehabilitation and follow-up monitoring of APL patients. Follow-up monitoring includes systematic examinations and targeted laboratory and instrumental evaluations aimed at assessing the remission status of the underlying disease and potential complications associated with prior polychemotherapy.

There are no special rehabilitation methods for APL.

Comments: after completing treatment, it is recommended to lead a healthy lifestyle and avoid sun exposure.

During polychemotherapy, cardio-, hepato-, neuro-, nephro-, and other toxicities are possible, the consequences of which may persist even after its completion.

5. Prevention and Dispensary Observation

Primary prevention of APL is impossible due to the low baseline incidence and undetermined causes of the disease.

Prevention of disease relapse is based on full adherence to the first-line therapy protocol and regular dynamic monitoring

1) complete blood count with differential count once every 3 months, then once every 6 months for 5 years;

2) molecular biological blood test for human immunodeficiency virus HIV-1, determination of hepatitis B virus surface antigen (HBsAg) in blood, determination of antibodies to hepatitis C virus in blood 6 months after the end of chemotherapy;

3) general biochemical blood test with evaluation of albumin, ALT, AST, LDH, bilirubin (total and direct), urea and creatinine, ferritin once a year for 5 years;

4) ECG and echocardiography once a year for 5 years;

GCR CLEL 5Grade of Recommendation C (Level of Evidence – 5)

6. Organization of Medical Care

Indications for planned hospitalization:

1) Suspicion/establishment of AL diagnosis

2) Diagnosis of APL relapse

3) Administration of the next course of chemotherapy in an inpatient setting

4) Performance of planned HSCT

5) Performance of planned surgical interventions,

6) Performance of planned extracorporeal blood purification methods and renal replacement therapy

7) Administration of replacement blood component therapy

Indications for emergency hospitalization:

Emergency conditions in APL patients and suspected AL:

- leukocytosis greater than 100 × 10⁹/L

- febrile neutropenia and infectious complications during neutropenia following a course of chemotherapy

- hemorrhagic syndrome

- thrombotic complications

- need for emergency blood component replacement therapy

- other systemic disorders caused by the course of the underlying disease or developed as a result of the treatment administered

Indications for patient discharge from the hospital:

1) Restoration of peripheral blood counts (leukocytes > 1×10⁹/L, granulocytes > 0.5×10⁹/L, platelets > 50×10⁹/L, hemoglobin > 80 g/L) after the next course of chemotherapy

2) Normothermia for 3–5 days and absence of uncontrolled infectious complications in the post-course period

3) Relief of hemorrhagic complications

4) Relief of thrombotic complications

5) Relief of systemic disorders caused by the course of the underlying disease or developed as a result of the treatment administered.

The conclusion regarding the feasibility of transferring the patient to a specialized medical organization is made after a prior consultation based on the provided medical documents and/or a preliminary examination of the patient by medical specialists of the medical organization to which the transfer is planned.

7. Additional Information

“Molecularly targeted” therapy

Progress in understanding the molecular pathogenesis of APL has led to the development of novel "molecular" drugs, i.e., molecules whose mechanism of action involves targeting proteins whose function is altered as a result of mutation or translocation (targeted therapy). For example, genetic alterations lead to mutations in genes activating signal transduction cascades (e.g., FLT3, KIT, RAS), gene fusions or mutations leading to increased or decreased transcriptional activity (e.g., PML-RARA, RUNX1-RUNX1T1, CBFB-MYH11, CEBPA), disruption of the function of genes involved in signal transmission (e.g., NPM1, NUP98, NUP), or overexpression of oncoproteins on the surface of APL cells. Although some molecularly targeted agents have demonstrated efficacy in APL, it was clear already at the clinical trial stage that most of them need to be used in combination with standard drugs. Currently, a large number of clinical trials are underway to study the efficacy in APL and safety of drugs from various pharmacological groups.

Criteria for Evaluating the Quality of Medical Care

References

Appendix A1. Working Group Composition

Maschan A.A. – MD, PhD, Professor, Director of the Institute of Hematology, Immunology and Cell Technologies, Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology of the Russian Ministry of Health, Professor at the Department of Hematology, Oncology and Radiation Therapy, Faculty of Pediatrics, Pirogov Russian National Research Medical University of the Ministry of Health of the Russian Federation

Aleinikova O.V. – MD, PhD, Professor, Corresponding Member of the National Academy of Sciences of Belarus, Head of the Department for the Implementation of National and International Projects in Pediatric Hematology and Oncology, Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology of the Russian Ministry of Health

Maschan M.A. – MD, PhD, Deputy General Director, Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology of the Russian Ministry of Health, Professor at the Department of Hematology, Oncology and Radiation Therapy, Pirogov Russian National Research Medical University of the Ministry of Health of the Russian Federation, Member of the Russian Society of Pediatric Oncologists and Hematologists

Novichkova G.A. – MD, PhD, Scientific Director, Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology, Russian Ministry of Health; Professor, Department of Hematology, Oncology and Radiation Therapy, Pirogov Russian National Research Medical University (RNIMU)

Popa A.V. – MD, PhD, Head of the Department of Epidemiology and Late Effects Studies in Childhood Cancer Survivors, Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology, Russian Ministry of Health; Professor, Department of Propaedeutics of Childhood Diseases, Pirogov Russian National Research Medical University (RNIMU)

Solopova G.G. – PhD in Medicine, Deputy Chief Medical Officer for Infection Control, Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology of the Russian Ministry of Health

Rumyantsev A.G. – MD, PhD, Academician of the Russian Academy of Sciences, President of Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology, Russian Ministry of Health; Professor, Department of Hematology, Oncology and Radiation Therapy, Pediatric Faculty, Pirogov Russian National Research Medical University

Valiev T.T. – MD, PhD, Head of the Hematology Department, Durnov Research Institute of Pediatric Oncology and Hematology, N.N. Blokhin National Medical Research Center of Oncology, Russian Ministry of Health.

Sadovskaya M.N. – Hematologist, Department of Pediatric Hematology/Oncology, Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology, Russian Ministry of Health

Abrosimov A.B. – PhD, Head of Department, Hematologist at the Department of Treatment and Rehabilitation of Immunohematological Patients and Stem Cell Recipients, Senior Researcher at the Laboratory of Pharmacology and Health Technology Assessment, Dmitry Rogachev National Medical Research Center of Pediatric Hematology, Oncology and Immunology, Russian Ministry of Health

No conflict of interest.

Appendix A2. Methodology for Developing Clinical Guidelines

Target audience of the clinical guidelines:

1. Hematologists;

2. Oncologists;

3. Pediatricians;

4. Anesthesiologists-intensivists;

5. Clinical pharmacologists.

Methodology for evidence collection

Methods used for evidence collection/selection:

Search for publications in specialized peer-reviewed periodicals;

Search in electronic databases.

Databases used for evidence collection/selection:

The evidence base for the guidelines includes publications indexed in the Cochrane Library, PUBMED, and MEDLINE databases. The search depth was 30 years.

Methods used for analyzing evidence:

• Reviews of published meta-analyses;

• Systematic reviews with evidence tables.

Methods used for assessing the quality and strength of evidence:

• Expert consensus;

• Evaluation of the significance of evidence in accordance with the evidence rating scheme (Tables A2.1–A2.3).

Table A2.1. Scale for grading levels of evidence (LE) for diagnostic methods (diagnostic interventions)

Table A2.2. Level of Evidence (LoE) grading scale for preventive, therapeutic, and rehabilitative methods (interventions)

Table A2.3. Grade of Recommendation (GoR) grading scale for preventive, diagnostic, therapeutic, and rehabilitative methods (interventions)

Procedure for updating clinical guidelines.

Updates are performed at least once every three years, taking into account new information on the diagnosis and management of patients with acute promyelocytic leukemia (APL). The decision to update is made by the Russian Ministry of Health based on proposals submitted by professional medical non-profit organizations. The submitted proposals must take into account the results of comprehensive assessments of medicinal products and medical devices, as well as the results of clinical approbation.

Appendix A3. Reference Materials

Appendix A3.1. Diagnostic tests and examinations used in patients with newly diagnosed APL

Appendix A3.2. Molecular genetic prognostic risk factors in APL

Table A3.3. Molecular genetic and clinical features of APL dividing patients into favorable and unfavorable prognostic groups [44]

Appendix A3.3 Diagnosis of infectious complications

Table A 3.4

Appendix B. Physician Action Algorithms

Appendix C. Patient Information

Acute myeloid leukemia is a rare malignant disease of the hematopoietic tissue characterized by uncontrolled proliferation, impaired differentiation, and accumulation of immature hematopoietic cells in the bone marrow and peripheral blood

When APL develops, all organs and systems are affected because the disease is generalized (disseminated). The clinical presentation is dominated by syndromes associated with the progressive increase in the number of malignant cells in the bone marrow, as well as in the liver and spleen; CNS involvement and lesions of other organs and systems are also possible. The most common manifestations of the disease include:

1) Fever.

An increase in body temperature above 38.0 °C can be the first and only manifestation of the disease due to the presence of blast (tumor) cells, the release of their metabolic products, and the development of an infectious process

2) Infectious process (tonsillitis, stomatitis, pneumonia, etc.) develops due to the displacement of normal hematopoietic cells—leukocytes/neutrophils—by blast cells, which normally protect a child's body from bacterial and fungal infections.

3) Hemorrhagic syndrome (bleeding, bruising) resulting from the displacement of platelets (cells responsible for stopping bleeding) from normal hematopoiesis by blast cells.

4) Anemic syndrome (pallor, lethargy, rapid fatigue, weakness), which also develops due to the lack of erythrocytes (decreased hemoglobin) in the bone marrow of a patient with APL.

5) Bone pain and pain in other affected organs

6) Enlargement of the liver and spleen, onset of jaundice.

7) CNS involvement may manifest as headache, vomiting, and seizures

Establishing a diagnosis requires a wide range of blood tests, bone marrow puncture, lumbar puncture, as well as X-ray and tomographic imaging. Chemotherapy requires the placement of a central venous catheter (CVC) to avoid numerous punctures of peripheral veins.

All invasive procedures (punctures, CVC placement) are performed under general anesthesia.

Treatment of acute myeloid leukemia generally consists of two phases: intensive therapy and hematopoietic stem cell transplantation. During the intensive phase, chemotherapy is administered at short intervals, and hospitalization is frequently required. First-line chemotherapy consists of three main drugs: cytarabine, etoposide, daunorubicin** (idarubicin** or mitoxantrone). This is followed by several courses of high-dose chemotherapy.

Side effects of chemotherapy:

1. Hair loss

2. Nausea and vomiting

3. Decreased/changed appetite

4. Fever

5. Development of infectious foci

6. The goal of therapy is to cure the disease, prevent relapses and complications associated both with disease manifestations and with the development of therapy-induced hematopoietic aplasia. The total duration of therapy is about 6 months without HSCT. Reducing the duration of therapy may increase the risk of disease relapse. When treated in accordance with modern treatment regimens, the probability of recovery is about 70%.