Phase 2 study of bosutinib in Japanese patients with newly diagnosed chronic phase chronic myeloid leukemia

This open-label, single-arm, phase 2 study (ClinicalTrials.gov, NCT03128411) evaluated the efficacy, safety, and pharmacokinetics of bosutinib at a starting dose of 400 mg once daily (QD) in Japanese patients with newly diagnosed chronic phase chronic myeloid leukemia (CP CML). The primary endpoint was major molecular response (MMR) at Month 12 in the modified as-treated population (Philadelphia chromosome-positive [Ph+] patients with e13a2/e14a2 transcripts). Sixty Japanese patients with CP CML were treated with bosutinib; median age was 55 years (range 20–83), 60.0% were males, and all were Ph+ and had e13a2/e14a2 transcripts. After median follow-up of 16.6 months (range 11.1–21.9), 41 (68.3%) patients remained on bosutinib. The MMR rate at Month 12 was 55.0% (2-sided 90% confidence interval: 44.4–65.6). There were no on-treatment transformations to accelerated/blast phase, and no patient died on treatment or within 28 days of the last bosutinib dose. The most common treatment-emergent adverse events were diarrhea (86.7%), increased alanine aminotransferase (55.0%), and increased aspartate aminotransferase (46.7%). The primary objective of this phase 2 study was met, and there were no new safety signals for bosutinib. These data suggest bosutinib is an effective first-line treatment option for Japanese patients with newly diagnosed CP CML.