A phase 1/2 study of bosutinib in Japanese adults with Philadelphia chromosome-positive chronic myeloid leukemia

Chiaki Nakaseko, Naoto Takahashi, Kenichi Ishizawa, Yukio Kobayashi, Kazuteru Ohashi, Yasunori Nakagawa, Kazuhito Yamamoto, Koichi Miyamura, Masafumi Taniwaki, Masaya Okada, Tatsuya Kawaguchi, Atsushi Shibata, Yosuke Fujii, Chiho Ono, Kazunori Ohnishi

This phase 1/2 study evaluated the safety and pharmacokinetics (part 1) and efficacy and safety (part 2) of bosutinib in Japanese Philadelphia chromosome-positive (Ph+) chronic-phase (CP) or advanced-phase chronic myeloid leukemia (CML) patients resistant/intolerant to previous imatinib (2L) or imatinib+dasatinib/nilotinib (3L). Based on dose-limiting toxicities and previous studies, the part 2 bosutinib starting dose was 500 mg/day (n = 63). For CP CML 2L (n = 28), the cumulative major cytogenetic response (MCyR) rate by week 24 was 36 % (primary endpoint); the cumulative major molecular response (MMR) rate through the study was 43 %. Transformation to accelerated/blast phase (AP/BP) was observed in one patient. Progression-free survival (PFS) and overall survival (OS) rates at 96 weeks were 94 and 96 %, respectively. Of seven advanced-phase 2L patients, one had confirmed complete hematologic response at week 84, and one had AP/BP transformation. PFS and OS rates at week 96 were 21 and 43 %. For 3L (n = 11), cumulative MCyR rate by week 24 was 18 %; cumulative MMR rate was 18 %; no transformations occurred. Common non-hematologic adverse events (AEs) were diarrhea (95 %), rash (57 %), and nasopharyngitis (51 %). Sixteen patients discontinued due to adverse events; no deaths occurred within 30 days of the last dose. Bosutinib 500 mg/day demonstrated efficacy and manageable toxicity in Japanese Ph+ CML patients resistant/intolerant to imatinib.