Background: Dasatinib (DAS) dose modifications generally mitigate adverse events (AEs) without affecting efficacy for responding patients (pts). A 2-year retrospective analysis of DASISION showed that rates of cytogenetic and molecular responses remained higher for pts given DAS vs imatinib (IM), even when daily doses were modified (Jabbour ASH 2011). Efficacy was not compromised due to dose reductions to manage DAS-related AEs. Here, we report results from a 5-year analysis evaluating the impact of dose reductions on efficacy in pts from DASISION. Methods: In DASISION (NCT00481247), pts with treatment-naïve CML-CP were randomized to receive either DAS (100 mg once/day; N = 259) or IM (400 mg once/day; N = 260). Up to 2 dose reductions were permitted for AEs (DAS: 80 mg, then 50 mg; IM: 300 mg, then 200 mg). Efficacy in all pts was evaluated retrospectively by 5 years. Results: Molecular response rates remained higher for DAS than IM, independent of dose reductions, and were comparable in pts with and without dose modifications in each arm (table). Overall, 95 (37%) DAS- and 44 (17%) IM-treated pts had dose reductions at any time due to AEs. Median average daily dose was 83 mg DAS and 328 mg IM for pts with reductions for any cause and 82 mg DAS for pts with reductions due to pleural effusion. The most common AEs resulting in dose reduction were hematological toxicity for IM (9%) and pleural effusion for DAS (12%). Conclusions: A 5-year retrospective analysis of DASISION showed molecular responses remained higher for DAS vs IM when daily doses were modified due to AEs. Dose reductions for any cause, including pleural effusion, did not affect efficacy (MMR rates were not reduced). In this analysis, for pts who experienced AEs, DAS dose reductions to 80 mg or 50 mg were safe and effective treatment options. Clinical trial information: NCT00481247

MMR, major molecular response; MR⁴, 4-log reduction in BCR-ABL1 transcripts.