Imatinib for newly diagnosed chronic-phase chronic myeloid leukemia: results of a prospective study in Japan

Although imatinib has become the current standard treatment for chronic myeloid leukemia (CML), there is limited information regarding its efficacy and safety among Japanese patients. We therefore conducted a prospective multi-center open-label study of imatinib for Japanese patients with newly diagnosed chronic-phase CML (CP-CML). A total of 107 patients were enrolled and treated with imatinib at an initial daily dose of 400 mg. Eighty-three patients completed 3 years of study treatment. The cumulative rates of major cytogenetic response and complete cytogenetic response (CCyR) were 90.9 and 90.2% at 3 years, respectively. The safety profile was not very different from that reported in the IRIS study, although grade ≥3 neutropenia occurred relatively frequently (31.8 vs. 14.3%). Only seven patients discontinued the study due to adverse events, as did four patients due to insufficient efficacy. The 3-year probabilities of overall survival and progression-free survival were 93.2 and 91.4%, respectively. Higher average daily doses (i.e., ≥350 mg) were significantly associated not only with higher rates of achieving CCyR, but also with longer duration of CCyR. These findings confirm the clinical utility of imatinib in Japanese patients with newly diagnosed CP-CML, and suggest detrimental effect of low average daily dose on treatment results.