- Acute Leukemias are rapidly progressive diseases caused by neoplastic proliferation of immature hematopoietic cells. Different subtypes of acute leukemias exist depending on the likely neoplastic cell of origin and are discussed on their own pages. However, all acute leukemias exhibit some common features that are discussed here.
- Acute leukemias likely derive from cells that develop during the early stages of hematopoiesis, termed "blasts". These early-stage cells normally divide very rapidly, likely accounting for their explosive growth once neoplastic. Early on, neoplastic blasts proliferate in the bone marrow and then spill out into the peripheral blood as well as solid lymphoid organs such as the spleen, lymph nodes, and liver. Consequently, the symptomology associated with these diseases is largely due to marrow and solid lymphoid organ infiltration.
- Neoplastic blasts have unique morphological features regardless of their particular subtype. In general, blasts are large cells with large nuclei, containing a fine granular chromatin and visible nucleoli. The bone marrow is usually effaced with sheets of neoplastic cells and a variable number can be seen in the peripheral blood. Typically, immunophenotyping of surface markers is used to confirm what blast subtype is present.
- The presentation of most acute leukemias is similar and is due to marrow and solid lymphoid organ infiltration as discussed above. Marrow infiltration often results in a myelophthisic anemia and thus pancytopenia, with attendant symptomology. In some cases, marrow infiltration can be so severe that patients experience bone pain. Additionally, generalized painless lymphadenopathy as well as hepatomegaly or splenomegaly can be presenting symptoms. In a minority of cases seeding of the CNS can yield neurological impairments as well as symptomology associated with increased intracranial pressure.
- Acute leukemias are subdivided by the particular cell lineage from which they are derived. Two major forms are Acute Lymphocytic Leukemia (ALL) which derives from a lymphocytic precursor, and Acute Myeloid Leukemia (AML) which derives from a myeloid precursor. In general, ALL is seen in children, while AML presents in adults.