Epidemiology and clinical features
The incidence of various types of mesenchymal neoplasms varies. Their clinical properties directly depend on histogenesis, specific localization in the body, as well as the patient's sex and age.
- Lipomas: These are the most common tumors, accounting for about one-third of all soft tissue tumors. As a rule, they are completely painless and are diagnosed predominantly in adult patients. Localization on the hands or lower extremities is extremely rare.
- Multiple angiolipomas: Unlike classic lipomas, these masses are painful upon palpation. They are most typical for young men.
- Vascular tumors: They account for approximately 10% of all cases. The overwhelming majority of such neoplasms are detected in childhood and in individuals under 20 years of age.
- Angioleiomyomas: They predominantly affect the lower extremities and are most commonly diagnosed in middle-aged women.
Etiology and pathogenesis
The etiology of most mesenchymal tumors remains undetermined. Pathogenesis is also not fully defined, but it is believed that the overwhelming majority of sarcomas arise primarily, i.e., de novo. At the same time, there is scientific evidence confirming the existence of a presarcoma stage, which is characterized by the gradual accumulation of genetic alterations (mutations) in cells.
Several key risk factors and associations are distinguished:
- Chemical carcinogens: Contact with dioxins contained in herbicides and plastics reliably increases the risk of developing sarcomas.
- Radiation exposure: Associated with the appearance of post-radiation malignant histiocytomas and osteosarcomas.
- Viral agents: The oncogenic role of herpesviruses and Epstein-Barr virus (EBV) has been proven.
- Hereditary predisposition: Familial cases of lipomas and angiolipomas have been described. In addition, sarcomas frequently develop against the background of severe genetic syndromes, such as Li-Fraumeni syndrome (associated with a mutation in the TP53 suppressor gene) and hereditary retinoblastoma (caused by a mutation in the Rb suppressor gene).
Benign tumors
Among benign mesenchymal neoplasms, adipose tissue tumors dominate. The primary and most frequent type is lipoma. In addition to it, there is a spectrum of related pathologies: lipomatosis, lipoblastoma (and lipoblastomatosis), angiolipoma, myolipoma, hibernoma, as well as specific variants—chondroid, spindle cell, and pleomorphic lipomas.
The most common benign tumor overall is recognized to be leiomyoma. It typically localizes in the uterus, gastrointestinal tract, and urinary bladder. An important feature is its histogenesis: regardless of the affected organ, leiomyoma develops from vascular wall pericytes. In cases where uterine leiomyomas have a highly developed connective tissue stroma, a more precise term is used—leiomyofibromas.
Malignant tumors (Sarcomas)
Malignant mesenchymal tumors are grouped under the general term sarcomas. They possess pronounced features of malignancy. Rapid infiltrative growth with destruction of surrounding tissues and early hematogenous metastasis are typical for them. Prominent secondary changes are frequently observed within the tumor node: extensive areas of tissue necrosis, myxoid change, massive hemorrhages, and calcification.
A separate important group consists of liposarcomas—malignant counterparts of adipose tumors. Depending on their histological structure, they are classified into several types:
- Well-differentiated.
- Dedifferentiated.
- Myxoid.
- Pleomorphic.
- Mixed-type liposarcoma.
Hereditary cancer syndromes
According to the WHO classification, there is a distinct group of hereditary syndromes in which tumors develop in endocrine organs. The main syndromes include multiple endocrine neoplasia (MEN) type 1, MEN type 2 (including types 2, 2A, and 2B), neurofibromatosis type 1, and hyperparathyroidism-jaw tumor syndrome.
Special attention in clinical practice is deserved by MEN type 2 (Sipple syndrome). This is a disease with an autosomal dominant inheritance pattern. It is based on a germline mutation of the RET proto-oncogene (Rearranged during Transfection). A synonym for the pathology is the term "multiple endocrine adenomatosis".
Clinical manifestations include the classical triad:
- Thyroid tumors (in the form of medullary carcinoma).
- Adrenal tumors (pheochromocytomas).
- Primary hyperparathyroidism (parathyroid gland involvement).
The syndrome occurs with a frequency of 1.25 to 7.5 cases per 10,000,000 population. Notably, it accounts for 25% of all hereditary forms of medullary thyroid carcinoma. The disease may occur with concomitant pathologies: Hirschsprung's disease and cutaneous amyloidosis. Diagnosis is based on a combination of clinical manifestations and the mandatory detection of the RET gene mutation.
Briefly: answers to topical questions
By what pathways do soft tissue sarcomas metastasize?
Soft tissue sarcomas metastasize predominantly via the hematogenous route, although lymphatic spread is also possible.
- Hematogenous route—transfer of neoplasm cells with the bloodstream. This is the most frequent pathway for sarcomas; metastases appear early.
- Lymphatic route—transfer of tumor cells with lymph flow. It occurs less frequently, but is characteristic of certain types (e.g., synovial sarcoma rapidly gives rise to both hematogenous and lymphatic metastases).
Which tumors are characteristic of MEN type 1 syndrome?
MEN type 1 syndrome is characterized by the development of tumors in various endocrine organs.
- Gastroenteropancreatic tumors—gastrinoma, glucagonoma, insulinoma, VIPoma, pancreatic polypeptide tumor, somatostatinoma.
- Pituitary tumors—prolactinoma, somatotropinoma, corticotropinoma, thyrotropinoma, non-functioning adenoma.
- Tumors of other localizations—adrenal tumors, thyroid tumors, bronchial and thymic carcinoids, neuroendocrine tumors of the stomach and duodenum, lung tumors.
Also typical for the syndrome is parathyroid hyperplasia leading to hyperparathyroidism.
What histological variants of leiomyoma exist?
Several histological variants of leiomyoma are distinguished, differing in structure and cellular composition.
- Simple leiomyoma—consists of bundles of smooth muscle cells running in various directions.
- Cellular leiomyoma—characterized by a high content of smooth muscle cells and poor development of connective tissue.
- Epithelioid leiomyoma—includes leiomyoblastoma, clear cell, and plexiform leiomyomas.
- Bizarre leiomyoma—characterized by the presence of giant symplast-like cells.
- Mitotically active leiomyoma—characterized by increased mitotic activity without cellular atypia.
- Lipoleiomyoma—contains mature fat cells.
Which genetic syndromes increase the risk of developing sarcomas?
The risk of developing sarcomas is increased by hereditary syndromes associated with mutations in tumor suppressor genes.
- Li-Fraumeni syndrome—an autosomal dominant disorder associated with a mutation in the TP53 suppressor gene (p53). This syndrome carries an increased risk of developing sarcomas and osteosarcomas.
- Hereditary retinoblastoma—a disease caused by mutations in the Rb suppressor gene, predisposing to the development of sarcomas.
The triad of Sipple syndrome (MEN 2): Thyroid, Adrenal, Parathyroid. Remember as TAP — Thyroid gland (medullary carcinoma), Adrenals (pheochromocytoma), Parathyroid glands (hyperparathyroidism).
Class and exam questions
From which cells does a leiomyoma develop?
Regardless of the affected organ (uterus, GI tract, or urinary bladder), leiomyomas originate from vascular wall pericytes.
What is the most frequent metastasis pathway for sarcomas?
Sarcomas are characterized by an early hematogenous metastasis pathway, meaning tumor cells spread throughout the body via blood vessels.
What is a leiomyofibroma?
This is a uterine leiomyoma, which is characterized by a well-developed connective tissue stroma.
What else to study on this topic
- Histological features of various types of liposarcomas
- Mechanisms of development of post-radiation malignant histiocytomas
- Role of herpes viruses and Epstein-Barr virus in the oncogenesis of mesenchymal tissues
- Clinical manifestations of Hirschsprung's disease in MEN syndrome type 2
- Differences between multiple endocrine neoplasia syndromes types 1 and 2
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