Diagnosis And Classification

Once the diagnosis of acute leukemia is suspected on the basis of abnormal blood counts, immature cells appearing in the peripheral blood differential, or the finding of extramedullary leukemia (especially in central nervous system, gums, or meninges, particularly in patients with monocytic subtypes), one should undertake a full diagnostic work-up that includes delineation of the AML subtype, as well as the definition of the risk group. In fact, the classification system for AML is evolving from the cytochemical and morphologically based French—American—British scheme5 to the cytogenetically centered World Health Organization (WHO) system.6 The WHO classification system acknowledges the critical impact of cytogenet-ics on prognosis as well as our improved pathophysio-logical understanding based on genes at balanced translocation breakpoints.

Although most subtypes of AML are treated in a similar fashion at least initially, it is important to recognize the 10-15% of AML patients who have acute promye-locytic leukemia (APL),7 characterized by malignant cells that appear as heavily granule-laden malignant promyelocytes with frequent Auer rods. These heavily myeloperoxidase-positive APL cells generally possess the characteristic t(15;17) cytogenetic abnormality, with a resultant PML-RARA rearrangement detectable on reverse transcription polymerase chain reaction analysis. APL is treated in a distinct fashion (see Chapter 6).

In addition to the definition of the AML subtype and risk strata, it is imperative to assess the underlying medical state of the patient, determining if any issues such as cardiac, renal, or pulmonary dysfunction might compromise the ultimate therapeutic plan. Finally, given the possibility that the patient might become a candidate for allogeneic stem cell transplant at some point, patient and sibling HLA typing should be carried out shortly after diagnosis.

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