Background:Ibrutinib (I) and venetoclax (V) improve chronic lymphocytic leukemia (CLL) outcomes compared to chemo-immunotherapy. We hypothesized I+V is more effective than fludarabine-cyclophosphamide-rituximab (FCR), and personalizing treatment duration, using measurable residual disease (MRD), would optimize outcomes.Methods:FLAIR, a phase III, multicenter, randomized, controlled, open-label platform trial for untreated CLL, compared I+V and I, to FCR. In I+V, after 2m I, V was added for up to 6y of therapy. The duration of I+V was defined by MRD assessed in peripheral blood (PB) and bone marrow (BM) and was double the time to undetectable MRD (uMRD). The primary endpoint was progression-free survival for I+V vs FCR, reported herein. Key secondary endpoints were overall survival, response, MRD and safety. Results:523 participants were randomized to FCR or I+V. At median 43.7m, there were 87 progressions (75 FCR, 12 I+V). The hazard ratio (HR) for progression-free survival for I+V vs FCR is 0.13 (95% confidence interval [CI], 0.07-0.24; P<0.0001). There were 34 deaths (25 FCR, 9 I+V). The HR for overall survival for I+V vs FCR is 0.31 (95%CI, 0.15-0.67). At 3y, 58.0% I+V participants stopped therapy due to uMRD. After 5y of I+V, 65.9% and 92.7% participants were BM and PB uMRD, respectively. Infection rates were similar. There were more cardiovascular events with I+V (10.7%) vs FCR (0.4%). Conclusion:MRD-directed I+V improved progression-free survival and favored overall survival compared to FCR. (Funded by Cancer Research UK and others; Trial Registration number: ISRCTN01844152 and EudraCT, 2013-001944-76.) <br/
