An Ongoing Phase 3 Study of Bosutinib (SKI-606) Versus Imatinib In Patients with Newly Diagnosed Chronic Phase Chronic Myeloid Leukemia

Abstract 208

Bosutinib is an orally bioavailable dual Src/Abl tyrosine kinase inhibitor (TKI), with minimal inhibitory activity against PDGFR or c-kit. In a phase 2 study, bosutinib demonstrated activity in patients with Philadelphia chromosome–positive (Ph+) chronic phase (CP) chronic myeloid leukemia (CML) in the second- and third-line treatment settings (Cortes JE, et al. ASCO 2010, Abstract #6502; Khoury JH, et al. ASCO 2010, Abstract #6514), as well as in patients with advanced Ph+ leukemias (Gambacorti-Passerini C, et al. ASCO 2010, Abstract #6509) following resistance or intolerance to imatinib and other TKIs. The current randomized, open-label, phase 3 study compared the activity and safety of bosutinib with that of imatinib in newly diagnosed patients with CP CML. The study enrolled adults aged ³18 years with cytogenetic diagnosis of Ph+ CP CML within 6 months, adequate hepatic and renal function, and an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1. Patients were randomized to daily oral treatment with 500 mg bosutinib or 400 mg imatinib. Adverse events were graded using the National Cancer Institute Common Terminology Criteria, version 3.0. The primary efficacy endpoint was the rate of complete cytogenetic response (CCyR) at 1 year; the rates of hematologic response, molecular response, and progression and transformation to accelerated or blast phase were also evaluated. The study randomized 502 patients: 56.6% male, median age of 48 years (range, 18–91 years), and median time since diagnosis of 0.7 months (range, -0.3-7.9 months; the range minimum is negative due to CML diagnosis during the study screening period, and the range maximum is >6 months because of 1 patient considered a major protocol violator). The median duration of treatment was 11.1 months (range, 0.03–24.8 months). At Week 48 (approximately 11 months), 71.5% and 74.8% of patients (both treatment arms combined) were in CCyR and complete hematologic response (CHR), respectively. During the study, 81.4% of patients achieved a CCyR at or before Week 48, with a median time to CCyR of 24 weeks; 82.6% of patients achieved a CHR, with a median time to CHR of 8 weeks; and 40.6% of patients achieved a major molecular response (MMR), with a median time to MMR of 49 to 61 weeks for the 2 treatment arms. For the combined treatment arms, common treatment-emergent adverse events included diarrhea (43.7%), nausea (32.3%), vomiting (22.0%), rash (16.8%), pyrexia (11.6%), and fatigue (11.0%). The only grade ³3 treatment-emergent adverse event observed in ³2% of patients was diarrhea (5.2%), which was usually limited to the first weeks of treatment. Grade ³3 hematologic laboratory abnormalities included neutropenia (14.2%), thrombocytopenia (12.4%), and anemia (5.8%). Other grade ³3 laboratory abnormalities (³5% of patients) included alanine aminotransferase elevation (11.6%), phosphatemia (7.6%), and aspartate aminotransferase elevation (6.4%). Overall, 22.2% patients discontinued therapy; adverse events led to discontinuation or death in 12.8% of patients, and 4.2% of patients discontinued due to disease progression. The high combined percentage of patients achieving MMR, CCyR, and CHR and the relatively low incidence of generally manageable grade ³3 events observed suggest good efficacy and an overall favorable safety profile. Data for individual treatment arms will be unblinded by the end of August 2010, and will be presented at the meeting.