Background: Bosutinib (BOS) is approved for the treatment (Tx) of Philadelphia chromosome–positive (Ph+) chronic myeloid leukemia (CML) resistant/intolerant to prior therapy and newly diagnosed Ph+ chronic phase (CP) CML. Body mass index (BMI) was shown to influence Tx response with front-line dasatinib vs imatinib (IMA). We report the efficacy and safety of BOS and IMA by BMI in patients (pts) with newly diagnosed CP CML. Methods: In the open-label BFORE trial, pts were randomized to receive 400 mg once daily BOS or IMA. Outcomes were assessed according to baseline BMI ≥25 or = 25 kg/m². This post hoc analysis was based on the final 5-y analysis (database lock: June 12, 2020). Results: In the BOS and IMA arms, respectively, 149 (56.4%) vs 115 (43.6%) pts and 145 (54.3%) vs 122 (45.7%) pts had BMI ≥25 vs = 25. In both the BOS and IMA arms, median Tx duration and time on study was 55 mo for pts with BMI ≥25 or = 25; respective median dose intensity was 394 vs 393 mg/d and 400 vs 400 mg/d. Molecular response (MR) rates are shown in the table. Cumulative incidence of major MR was similar in pts with ≥25 vs = 25 receiving BOS (HR 0.99; 95% CI 0.74−1.31) or IMA (HR 1.09; 95% CI 0.81−1.47). Event-free survival (EFS) and overall survival (OS) rates at 60 mo are shown in the table. Most common reasons for Tx discontinuation were adverse events (AEs) (BOS 28.2 vs 20.0%; IMA 13.3 vs 10.7%) and lack of efficacy (BOS 5.4 vs 5.2%; IMA 16.1 vs 19.8%). In pts with BMI ≥25 vs = 25, dose reductions and interruptions due to Tx-emergent AEs (TEAEs) occurred in 43.6 % vs 46.2% and 66.4% vs 69.7% of pts with BOS and 24.5% vs 24.6% and 40.6% vs 50.8% with IMA. Any grade TEAEs in ≥30% of pts with BMI ≥25 vs = 25 were diarrhea (73.8 vs 73.1%), nausea (40.9 vs 31.9%), thrombocytopenia (30.9 vs 41.2%), increased alanine (37.6 vs 28.6%) and aspartate aminotransferase (30.2 vs 20.2%) with BOS and diarrhea (49.0 vs 29.5%), nausea (46.2 vs 37.7%), muscle spasms (33.6 vs 26.2%), neutropenia (14.7 vs 32.0%) and thrombocytopenia (10.5% vs 30.3%) with IMA. Conclusions: Efficacy of BOS was consistent in pts with BMI ≥25 or = 25; however, with IMA a low (vs high) BMI appeared to be associated with worse survival outcomes. Differences in certain TEAEs were observed between BMI subgroups in both treatment arms. Clinical trial information: NCT02130557

Note: OR > 1 and HR = 1 favor BMI ≥25 kg/m². * Adjusted for Sokal risk group and region as determined at randomization. MMR = major molecular response.