44. Leukemias – definition, etiology, pathogenesis, types · Pathophysiology · MU Plovdiv

Leukemias - definition, etiology, pathogenesis, types

⭐ Leukemias - malignant neoplasms of the white blood cell lineage derived from hematopoietic stem cells

They are characterised by diffuse replacement of bone marrow with unregulated, proliferating, immature neoplastic cells
In most cases, the leukemic cells spill out into the blood, where they are seen in large numbers
The leukemic cells may also infiltrate the liver, spleen, lymph nodes, and other tissues causing enlargement of these organs

The exact causes of leukemia are unknown
The incidence of leukemia among persons who have been exposed to high levels of radiation is high
An increased incidence of leukemia also is associated with exposure to benzene and the use of antitumor drugs
Leukemia may also occur as a second cancer after aggressive chemotherapy for other cancers, such as Hodgkin's disease
There is suggestions of a genetic predisposition for leukemia due to the increased leukemia incidence in individuals with diseases such as Down syndrome

The leukemias are commonly classified according to the predominant cell type (i.e. lymphocytic or myelogenous) and whether the condition is acute or chronic
A rudimentary classification system divides leukemia into four types:

The lymphocytic leukemias involve immature lymphocytes and their progenitors that originate in the bone marrow but infiltrate the spleen, lymph nodes, CNS and other tissues
The myelogenous leukemias, which involve the myeloid stem cells in bone marrow, interfere with the maturation of all blood cells, including the granulocytes, erythrocytes, and thrombocytes

The acute leukemias usually have a sudden and stormy onset of signs and symptoms
Acute lymphocytic leukemia (ALL) is the most common leukemia in childhood
ALL encompasses a group of neoplasms composed of immature precursor B or T lymphocytes
Acute myelogenous leukemia (AML) is chiefly an adult disease
Most cases of ALL are of pre-B-cell origin
The AMLs are an extremely heterogeneous group of disorders
Some arise from the pluripotent stem cells in which myeloblasts predominate, and others arise from the monocyte-granulocyte precursor
Clinical manifestations:
Warning signs = fatigue, pallor, weight loss, repeated infections, easy bruising
Generalised lymphadenopathy, splenomegaly, and hepatomegaly
Leukostasis - circulating blast count is elevated ( ~ 100,000 cells/μl) → increases blood viscosity → leukoblastic emboli