Uncontrolled clonal proliferation of white blood cells, particularly the immature precursors forms (called blasts).
They cause adverse effects by infiltration and displacement of the normal bone marrow cells producing blood dyscrasia. The symptoms depend on which component is most affected:
- All normal cells depleted - Pancytopenia
- Erythrocytes - Anaemia
- Leucocytes - Neutropenia
- Platelets - Thrombocytopenia
The clinical sequelae depends on the exact type of precursor cell as well as the rate of proliferation (which in turn affects the rate of bone marrow infiltration. Therefore, commonly classified as:
- Acute vs. Chronic
- Myeloid (or sometimes myelogenous) vs. Lymphoid (the precursor to lymphocytic cells; sometimes referred to as lymphocytic)
- Acute lymphocytic leukaemia
- Acute myeloid leukaemia
- Chronic lymphocytic leukaemia
- Chronic myeloid leukaemia
Others that don't fall neatly into classification
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