What constitutes a “remission” in AML? How does one know that a remission had been obtained? Not surprisingly, as befits this important question, International Working Group has enunciated criteria for defining a remission for AML. They are:
- Normal values for absolute neutrophil count (>1000/microL) and platelet count (>100,000/microL), and independence from red cell transfusion.
- A bone marrow biopsy that reveals no clusters or collections of blast cells. Extramedullary leukemia (e.g., central nervous system or soft tissue involvement) must be absent.
- A bone marrow aspiration reveals normal maturation of all cellular components (i.e., erythrocytic, granulocytic, and megakaryocytic series). There is no requirement for bone marrow cellularity.
- Less than 5 percent blast cells are present in the bone marrow, and none can have a leukemic phenotype (e.g., Auer rods). The persistence of dysplasia is worrisome as an indicator of residual AML but has not been validated as a criterion for remission status.
- The absence of a previously detected clonal cytogenetic abnormality (i.e., complete cytogenetic remission, CRc) confirms the morphologic diagnosis of CR but is not currently a required criterion. However, conversion from an abnormal to a normal karyotype at the time of first CR is an important prognostic indicator, supporting the use of CRc as a criterion for CR in AML.
Some patients may fulfill all of the above criteria for CR but may not recover normal peripheral blood counts. These are denoted as CRi, or CR with insufficient hematological recovery (platelets or neutrophils). CRp describes a subset of patients with CRi, wherein patients fulfill all criteria for CR except that platelet counts are <100,000/microL. Lack of full recovery of counts is of significant concern as it may presage relapse. The survival and relapse rates for patients with CRp appear to be worse than those with a CR, but better than those with a partial remission (PR).
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