Definition of oncology and its boundaries
Oncology is a branch of medicine that studies benign and malignant tumors, the mechanisms of their origin and development, as well as methods of prevention, diagnosis, and treatment. In the clinical practice of an oncologist, the main focus is precisely on diagnostic and treatment methods, whereas the molecular mechanisms of carcinogenesis are considered less frequently and are more theoretical in nature.
Oncology as a specialty deals primarily with solid tumors — neoplasms arising from "solid" tissues and organs that can be visualized and palpated. Diseases of the blood and lymphatic system fall under the purview of hematology, which has emerged as an independent specialty. Although drug treatment regimens may partially overlap, patient management approaches differ fundamentally; therefore, upon detecting a lymphoma, an oncologist refers the patient to a hematologist, whereas upon discovering a solid metastasis in a lymph node, a hematologist transfers the patient to an oncologist.
Internal structure of oncology
Oncology includes many subspecialties, each dealing with a specific group of tumors:
- neoplasms of the urinary tract and male reproductive organs are treated by a uro-oncologist;
- tumors of the female reproductive system — by a gyn-oncologist;
- neoplasms of the eye — by an ocular oncologist;
- primary tumors of the central nervous system (glioblastomas, astrocytomas) are treated by a neurosurgeon rather than a general oncologist.
Important terminological clarification: the term "cancer" applies only to malignant tumors developing from epithelial tissue. The expressions "blood cancer" or "brain cancer" are incorrect — in these cases, one speaks of lymphoma, leukemia, or malignant neoplasms of the corresponding nervous tissue. An exception has historically been established for renal cell carcinoma, which by origin is not epithelial in the classical sense, but is traditionally called kidney cancer.
Etiology of malignant tumors
In most cases, the exact cause of a specific tumor's development remains unknown; however, risk factors that reliably increase the probability of the disease have been identified: smoking, carcinogenic chemical compounds, and ionizing radiation. Among proven mechanisms, two directions stand out in particular — mutation and viral theories of carcinogenesis.
Mutation theory links tumor development to inherited genetic changes. A classic example is mutations in the BRCA1/BRCA2 genes, which reliably increase the risk of breast and ovarian cancer in women, and prostate cancer in men. Identifying significant mutations is important not only for prognosis: targeted drugs are developed based on them, such as olaparib, which increases treatment efficacy in BRCA mutation carriers.
Viral theory describes a group of oncoviruses with a proven carcinogenic role:
- Epstein-Barr virus — associated with Hodgkin lymphoma, Burkitt lymphoma, and nasopharyngeal carcinoma;
- human papillomavirus (HPV) — causes cervical cancer, as well as rarer tumors of the penis, anal canal, and vagina; vaccination significantly reduces this risk;
- Merkel cell polyomavirus — associated with a rare and aggressive cancer of skin appendages;
- hepatitis B and C viruses — increase the risk of hepatocellular carcinoma, which can develop both in young patients (aggressive course) and against the background of liver cirrhosis.
Precancerous conditions
Precancerous changes are divided into two types. Facultative precancers (dysplasias, polyps, and similar changes) occur frequently and require monitoring, and surgical removal if necessary. Obligate precancers have a high probability (about 90%) of progressing to a malignant tumor, but are significantly rarer and, as a rule, hereditary: familial adenomatous polyposis of the colon, xeroderma pigmentosum, Bowen's disease, Lynch syndrome.
Diagnosis in oncology
Most oncological diseases are asymptomatic in the early stages, which is why dispensary health examination (dispanserizatsiya) plays an important role as a tool for early detection. A classic example of screening is determining prostate-specific antigen (PSA) in older men followed by refining the data using magnetic resonance imaging of the prostate gland.
Computed tomography (CT) and MRI form the basis of visualization, but ultrasound examination is preferred for a number of localizations (thyroid gland, ovaries). Special grading scales are used to standardize the description of results, for example:
- TI-RADS — for the thyroid gland;
- BI-RADS — for the breast;
- PI-RADS — for the prostate gland.
These scales are graded from 1 (likely benign lesion) to 5 (high probability of malignancy), but the final diagnosis is established only on the basis of the histological report obtained from a biopsy. Instrumental methods, including PET-CT, provide grounds for suspicion but do not replace morphological verification, which is necessary for prescribing antineoplastic drug treatment.
Principles of treatment
Surgical tumor removal remains the gold standard of treatment for most solid neoplasms, provided the patient is operable and has a satisfactory performance status. Drug treatment (chemotherapy, targeted therapy) is used in several regimens:
- neoadjuvant therapy — performed before surgery to reduce tumor size;
- adjuvant therapy — prescribed after surgery to eliminate possible residual tumor cells;
- standalone drug treatment — used in widespread disease with multiple metastases, when surgical removal of all foci is impossible.
In the case of single distant metastases combined with a resectable primary tumor, combined surgical treatment of multiple localizations simultaneously is possible, but in multiple metastatic lesions, priority is given to systemic drug therapy.
Key points
- Oncology deals primarily with solid tumors; blood and lymphatic diseases belong to hematology.
- Within oncology, there are subspecialties — uro-oncology, gyn-oncology, ocular oncology, neurosurgery for CNS tumors.
- The term "cancer" applies only to epithelial malignant tumors; the expressions "blood cancer" and "brain cancer" are incorrect.
- The main proven mechanisms of carcinogenesis are mutation theory (BRCA1/2 and others) and viral theory (EBV, HPV, Merkel cell virus, hepatitis B and C).
- Precancerous conditions are divided into facultative (frequent, require monitoring) and obligate (rare, hereditary, with a high risk of malignancy).
- Dispensary health examinations and screening methods (e.g., PSA) help detect asymptomatic oncological diseases in early stages.
- Diagnosis is established solely on the basis of the histological report, despite the informativeness of CT, MRI, and PET-CT.
- Surgical tumor removal is the primary treatment method; drug therapy is used as neoadjuvant, adjuvant therapy, or as the main method in widespread disease.