Acute promyelocytic leukemia is the first malignant disease highly curable with targeted therapy directed at a unique molecular abnormality. The characteristic bleeding diathesis is the most notorious manifestation of the disease, which historically has accounted for a high mortality rate during induction. Acute promyelocytic leukemia is one of the few hematologic diseases that must be recognized under the microscope by the practicing hematologist because early institution of all-trans retinoic acid (ATRA) at the first suspicion of the disease before confirmation of the diagnosis and aggressive blood product support are critical to reduce early mortality. ATRA plus anthracycline-based chemotherapy for induction and consolidation followed by maintenance ATRA with low-dose chemotherapy is currently the standard of care. However, the combination of ATRA and arsenic trioxide, with minimal chemotherapy to control leukocytosis, is very effective therapy for newly diagnosed patients. This combination may replace conventional approaches for most, if not all, patients in the very near future. Acute promyelocytic leukemia should be considered in any patient with newly diagnosed acute myeloid leukemia because the treatment is urgent and different from all other subtypes. (Blood. 2009; 114:5126-5135)
IntroductionAcute promyelocytic leukemia (APL) is a subtype of acute myeloid leukemia (AML) with distinctive biologic and clinical features that is now highly curable. Most patients are young, present with leukopenia, and exhibit a life-threatening coagulopathy, which is the most notorious manifestation of the disease. The cells from almost all patients have a balanced reciprocal translocation between chromosomes 15 and 17, 1 which generates a fusion transcript joining the PML (promyelocyte) and RAR-␣ (retinoic acid receptor-␣) genes. 2 Leukemic promyelocytes have the unique ability to undergo differentiation with exposure to retinoic acid and both differentiation and apoptosis with exposure to arsenic trioxide (ATO). The disease is relatively rare in adults, accounting for only 10% to 15% of the approximately 13 400 adults diagnosed with AML in the United States each year. Although the incidence of APL among children with AML is similar in some series, a higher overall percentage of APL in children with AML compared with adults has been reported in others. 3 In children, the disease is often associated with a high white blood cell count (WBC Ͼ 10 000/ L), the microgranular variant (M3V), and more all-trans retinoic acid (ATRA)-related toxicities, particularly pseudotumor cerebri. 4 Intensive studies of the biology and treatment of the disease have resulted in a remarkably thorough understanding of its pathogenesis. 5 Furthermore, a cure rate of approximately 80% to 90% of patients who survive induction and achieve complete remission (CR) can be expected. 6 Yet there are nuances in the approach to patients with APL that are often overlooked, and complicated issues in treatment that remain to be studied. Here, the initial approa...