Study design. The number of patients who completed each step is indicated. C1, C2, and C3 were consolidation courses 1, 2, and 3. A total of 283 patients had t(15;17) and/or the PML-RARα transcript at the time of diagnosis, and 230 patients were negative for PML-RARα at the end of 3 courses of consolidation therapy. After completion of consolidation therapy, 175 patients who showed absence of PML-RARα transcript were randomized either to receive 6 courses of intensified maintenance chemotherapy (n = 89) or to observation (n = 86).