Primary results of the phase 4 BYOND study of bosutinib (BOS) for pretreated chronic phase (CP) chronic myeloid leukemia (CML).

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7012 Background: The tyrosine kinase inhibitor (TKI) BOS is approved for patients (pts) with Philadelphia chromosome (Ph)+ CML resistant/intolerant to prior therapy and newly diagnosed pts in CP. Methods: The ongoing phase 4 BYOND study is further evaluating efficacy and safety of BOS (starting dose 500 mg/d) for CML resistant/intolerant to prior TKIs. Primary endpoint (not powered) in Ph+ CP CML cohorts is cumulative confirmed major cytogenetic response (MCyR) by 1 y. Results: Of 163 pts who received BOS, 156 had Ph+ CP CML (46, 61 and 49 after 1, 2 and 3 prior TKIs, respectively). Across Ph+ CP CML cohorts, 51.9% of pts were male; median age was 61 y. As of 1 y after last enrolled pt (median follow-up 30.4 mo), 56.4% remained on BOS. Median BOS duration was 23.7 mo and median dose intensity after adjustment due to adverse events (AEs) 313 mg/d. Of 144 evaluable pts with a valid baseline assessment, cumulative confirmed MCyR by 1 y was 71.5% (95% confidence interval [CI] 63.4–78.7). Cumulative complete cytogenetic response rate anytime on treatment was 81.3% (95% CI 73.9–87.3). Cumulative molecular response (MR) rates were high across lines of therapy (Table). 10 deaths occurred (5 on treatment); 1-y overall survival rate was 98.0%. No pt progressed to accelerated/blast phase on treatment. 25.0% discontinued BOS due to AEs and 5.1% due to insufficient response. Most common treatment-emergent AEs (TEAEs) were diarrhea (87.8%) and nausea (41.0%). Grade 3/4 TEAEs in > 10% of pts were diarrhea (16.7%) and increased alanine aminotransferase (ALT; 14.7%). The only TEAE leading to discontinuation in > 5% of pts was increased ALT (5.1%). Conclusions: Most pretreated pts with Ph+ CP CML had MCyR by 1 y with BOS; a substantial proportion achieved or preserved major MR (MMR) and deep MR in all therapy lines. Results further support BOS use for Ph+ CP CML resistant/intolerant to prior TKIs. Clinical trial information: NCT02228382. [Table: see text]