Management of Acute Promyelocytic Leukemia

This chapter addresses the management of acute promyelocytic leukemia (APL), a unique subtype of acute myeloid leukemia characterized by a block at the promyelocyte stage of hematopoiesis. All-trans retinoic acid (ATRA) is the standard induction therapy, and it is typical to continue APL-focused therapy until molecular tests are available. Following induction chemotherapy, the leukemia promyelocytes differentiate into mature neutrophils. Differentiation can take weeks, so performing a bone marrow biopsy after induction often leads to confusion rather than clarity, with immature forms seen in the marrow; the authors do not perform a bone marrow biopsy until 4-6 weeks after induction chemotherapy has been completed. Although the cure rates for APL are remarkable, early death (within 30 days of diagnosis) remains the major cause of treatment failure, and the rate has not changed since the introduction of ATRA; in population-based studies, the early death rate ranges between 17% and 30%, and it is considerably higher in older patients. Patients with molecular relapse of APL will likely develop overt hematologic relapse. Because of this, intervention when the PML-RAR transcript level is rising is the accepted approach for patients with evidence of relapse.