HUMAN MEDICAL BIOLOGY, ANATOMY, PHYSIOLOGY AND PATHOLOGY - Y.I. Fedonyuk 2010

ANATOMY, PHYSIOLOGY, PATHOLOGY

SECTION 4. BLOOD SYSTEM

PATHOLOGY OF THE BLOOD SYSTEM

QUANTITATIVE BLOOD CHANGES

2. TUMORS OF THE BLOOD SYSTEM OR HEMOBLASTOSES

2.1. LEUKEMIAS

Leukemia is a disease characterized by the proliferation of hematopoietic Cells of neoplastic origin, known as leukemic cells. Initially, these cells proliferate in the Bone Marrow and subsequently spread via the bloodstream to other Organs and Tissues, where they form leukemic infiltrates.

Such leukemic infiltration causes enlargement, dystrophy, and atrophy of many Internal Organs. The relentless proliferation of leukemic cells suppresses erythropoiesis and cellular Immunity. Consequently, patients with leukemia develop severe anemia, hemorrhages, ulcerative-necrotic lesions, and Sepsis, which ultimately become the cause of death.

There are numerous factors capable of triggering the transformation (mutation) of normal Blood Cells into tumor cells. These factors are called mutagens and include Viruses, ionizing radiation, and certain chemicals.

Depending on the count of leukocytes and leukemic cells in peripheral blood, leukemia variants are classified as leukemic (hundreds of thousands or tens of thousands of leukocytes per 1 mкл of blood), subleukemic (no more than 15-25 thousand per 1 mкл of blood), leukopenic (leukocyte count below normal, yet leukemic cells are still detected), and aleukemic (leukemic cells are absent from the blood).

Based on the degree of Cell Differentiation (maturity) and the clinical course, all leukemias are divided into acute and chronic.

Acute leukemias are characterized by the proliferation of immature, poorly differentiated, or undifferentiated cells known as blasts. Therefore, they are referred to as "blastic". The differentiation of hematopoietic cells does not progress beyond Class IV cells. Since hematopoiesis at this level diverges into two lineages—myeloblastic and lymphoblastic—acute leukemias are likewise categorized into myeloblastic and lymphoblastic.

Chronic leukemias are characterized by the proliferation of differentiated (mature) cells, a relatively benign clinical course, and are referred to as "cytic". They are subdivided into myeloblastic and lymphoblastic. The course of chronic leukemias comprises two stages:

1) a benign or monoclonal stage, which lasts for years and responds well to medical management;

2) a malignant or polyclonal stage, in which chronic leukemia transforms into an acute form with the appearance of blasts. This transition into the Second Stage occurs abruptly and is termed a blast crisis.