Leukemia

Leukemia is a malignant tumor of leukocyte germ, involving the pathological process of bone marrow, circulating leukocytes and organs, for example the spleen and lymph nodes.

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The cause and pathophysiology of leukemia

Malignant transformation, as a rule, occurs at the level of pluripotent stem cells, although sometimes transformation occurs in committed stem cells with a more limited ability to differentiate. Abnormal proliferation, clonal expansion and oppression of apoptosis (programmed cell death) leads to replacement of normal cellular elements of blood with malignant cells.

The risk of developing the majority of leukemias increases with the presence of an exposure to ionizing radiation in the anamnesis (for example, after the atomic bombardment in the cities of Nagasaki and Hiroshima), chemical compounds (for example, benzene); treatment with some antitumor drugs, in particular procarbazine, nitrosourea derivatives (cyclophosphamide, melphalan) and epipodophyllotoxins (etoposide, teniposide); infection with viruses (eg, human T-lymphotropic virus types 1 and 2, Epstein-Barr virus); chromosomal translocations; a number of diseases, such as immunodeficiency states, chronic myeloproliferative diseases, chromosomal diseases (eg, Fanconi anemia, Bloom's syndrome, ataxia-telangiectasia, Down's syndrome, infantile X-linked agammaglobulinemia).

Clinical manifestations of leukemia are caused by oppression of the mechanisms of formation of normal cellular elements and infiltration of organs by leukemia cells. Leukemia cells produce inhibitors and replace normal cell elements in the bone marrow, which leads to suppression of normal hematopoiesis with the development of anemia, thrombocytopenia and granulocytopenia. Infiltration of organs leads to an increase in the liver, spleen, lymph nodes, sometimes affects the kidneys and gonads. Infiltration of the meninges leads to clinical manifestations, which are caused by increased intracranial pressure (for example, paralysis of the cranial nerves).

Classification of leukemia

Initially, the terms "acute" and "chronic" leukemia were related to the life expectancy of patients, and at present leukemia is classified according to the degree of cell maturity. Acute leukemias consist mainly of immature, slightly differentiated cells (usually blast forms); Chronic leukemia is characterized by more mature cells. Acute leukemias are subdivided into lymphoblastic (ALL) and myeloblastic (AML) types, which according to the Franco-American-British (FAB) classification are divided into subtypes. Chronic leukemias are divided into lymphocytic (CLL) and myelocytic (CML).

Myelodysplastic syndromes include states with progressive bone marrow deficiency, but with an insufficient proportion of blast cells (<30%) to explicitly match the diagnosis of "acute myeloblastic leukemia"; from 40 to 60% of cases myelodysplastic syndrome is transformed into acute myeloblastic leukemia.

The leukemoid reaction is expressed granulocyte leukocytosis (ie, the number of white blood cells> 30 000 / μL) produced by normal bone marrow in response to a systemic infection or cancer. Although it is not a neoplastic disorder, a leukemoid reaction with very high leukocytosis may require differential diagnosis with chronic myelogenous leukemia.

The Franco-American-British classification of acute leukemia (FAB classification)

Acute lymphoblastic leukemia

L1	Monomorphic lymphoblasts with a rounded nuclei and a small cytoplasm
L2	Polymorphic lymphoblasts with nuclei of various forms and large cytoplasm volume than with L1
L3	Lymphoblasts with small particles of chromatin in the nucleus and blue or dark blue cytoplasm with vacuolization

Acute myeloblastic leukemia

M1	Undifferentiated myeloblastic leukemia; there are no granules in the cytoplasm
M2	Myeloblastic leukemia with cell differentiation; poor granulation can be recorded both in individual cells and in a large number of them
MH	Promyelocytic leukemia; The granules are typical for promyelocytes
M4	Myelomonoblastny leukemia; mixed myeloblastic and monocytic morphology
M5	Monoblastic leukemia, mono-blast morphology
MB	Erythroleukemia; morphology of mostly immature erythroblasts, sometimes there are megaloblasts
M7	Megacaroblastic leukemia; cells with processes, budding can be noted

[3], [4], [5], [6], [7], [8], [9], [10], [11]