Background: Bosutinib (BOS) is approved for pts with Philadelphia chromosome-positive CML resistant/intolerant to prior therapy and newly diagnosed pts in chronic phase. Methods: The BYOND trial (NCT02228382) evaluated the efficacy and safety of BOS in 163 pts with CML resistant/intolerant to prior tyrosine kinase inhibitors (TKIs; Gambacorti-Passerini et al, Blood, 2021). We report a sub-analysis of 48 pts treated with 2 (3L) and 3 (4L) prior TKIs, categorized by resistance/intolerance to the last received TKI. This sub-analysis is based on the final Nov 23, 2020 database lock. Results: There were 18 and 30 pts resistant or intolerant to the last TKI who entered the study without complete cytogenetic response (CCyR) or major molecular response (MMR), respectively. Median (range) treatment duration was 10.6 mo (1.6–48.5) vs 28.3 mo (0.2–48.6) and median (range) dose intensity was 447.1 mg/d (131.3–520.4) vs 288.8 mg/d (79.7–500.0) for resistant vs intolerant pts. Prior TKIs included imatinib (88.9% vs 100.0%), dasatinib (88.9% vs 83.3%), and nilotinib (66.7% vs 63.3%) for resistant vs intolerant pts. Overall, 61.1% vs 66.7% of resistant vs intolerant pts discontinued BOS, mostly commonly due to adverse events (AEs) in 27.8% vs 16.7% pts; 16.7% vs 6.7% discontinued BOS due to insufficient clinical response. Rates of CCyR/MMR are shown in the table. Among responders (resistant vs intolerant pts), median (range) time to CCyR was 5.1 mo (2.8–8.8) vs 3.0 mo (2.7–6.1); median (range) time to MMR was 5.8 mo (2.8–9.4) vs 3.2 mo (2.8–9.3). In resistant vs intolerant pts, any grade treatment-emergent AEs (TEAEs) were reported by 100.0% vs 96.7% pts; grade 3/4 TEAEs were reported by 72.2% vs 83.3% pts. Grade 3/4 TEAEs > 10% in resistant pts were thrombocytopenia (22.2%) and neutropenia (11.1%), and in intolerant pts were increased alanine aminotransferase (26.7%), diarrhea (23.3%), pleural effusion (13.3%), and rash (13.3%). Conclusions: This sub-analysis of resistant/intolerant pts without baseline CCyR or MMR shows BOS was active in heavily pretreated pts with resistance/intolerance to the last TKI. Despite a difference between resistant/intolerant pts, efficacy outcomes, though lower than the overall BYOND population, are encouraging, and safety was generally consistent with previous reports. Clinical trial information: NCT02228382.

Evaluable pts had a valid baseline assessment. Resistant pts were excluded if they had baseline CCyR; intolerant pts were excluded if they had baseline MMR.