Maintenance Therapy

Data from two trials published in the mid-1990s suggested that maintenance therapy with ATRA and/or chemotherapy, generally 6-mercaptopurine (6-MP) plus methotrexate (MTX), was beneficial in increasing the cure rate of APL. For example, in the APL93 study, the 5-year risk of relapse was 39, 29, 24, and 13% in patients who received, respectively, no maintenance, ATRA alone, 6-MP/MTX alone, or combined ATRA/6-MP/ MTX.51 In the group of patients with high WBC count (more than 5000/^L in this study), the relapse risk was 47% without maintenance, but only 8% if patients received ATRA/6-MP/MTX.51 In the North American Intergroup 0129 study,30 5-year disease-free survival was 74% in patients who received ATRA during both induction and maintenance, compared to 55% for patients who received ATRA only during induction. In contrast to the above results, GIMEMA investigators27 found no differences in molecular disease-free survival according to any of the four maintenance arms (ATRA/6-MP/MTX, ATRA alone, 6-MP/MTX alone, or no maintenance). The ultimate role of maintenance therapy in APL may be difficult to precisely define, as its usefulness may depend on both patient-specific (i.e., risk category) and treatment-specific (i.e., intensity of induction and consolidation therapy) factors. However, currently, ATRA- or arsenic-trioxide-based maintenance therapy is strongly recommended for all patients, and it should be considered mandatory in high-risk patients. Commonly used regimens include 45 mg/m2/day of ATRA every other week, or ATRA at the same dose for 15 days out of each 3-month period. Standard maintenance doses of 6-MP and MTX are 60 mg/m2/day and 20 mg/m2/week, respectively. Treatment should be continued for at least 1 year, but 2 years may be preferable.51 Maintenance therapy is generally well tolerated, but serious complications can occur, particularly in patients receiving 6-MP and MTX (┬▒ATRA), and include abnormal liver function tests, cytopenias with potentially serious infections, and opportunistic infections such as Pneumocystis carinii pneumonia.51

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