Background: Ibr, a first-in-class, once-daily inhibitor of Bruton’s tyrosine kinase, is FDA-approved for all pts with CLL/SLL. We report updated safety and efficacy results with up to 4 y follow-up from the ph III RESONATE trial of ibr vs ofatumumab (ofa). Methods: Pts had ≥1 prior therapy. Pts received 420 mg ibr PO until PD or ofa up to 24 wks. At interim analysis (median 9 mo follow-up), the DMC declared superiority of ibr vs ofa for PFS and OS, and ibr access was recommended for all ofa pts. Long-term follow-up efficacy endpoints are per investigator assessment. Ofa pts were censored at crossover for OS. Results: 391 pts were randomized to receive ibr (n = 195) or ofa (n = 196). Median age was 67 y (40% ≥70 y); 57% had Rai stage III/IV. With median follow-up of 44 mo (53 mo max) for ibr arm, PFS was significantly longer for ibr vs ofa (median NR vs 8 mo, [HR 0.133; P< 0.0001]; 3-y PFS 59% vs 3%) with significant benefit across subgroups. PFS with ibr for del11q subgroup trended to have the most favorable outcome; however, PFS was not statistically different for pts with del17p or del11q or without these FISH abnormalities. At analysis, with the majority of pts (68%) randomized to ofa crossing over to ibr, OS was longer for ibr vs ofa (median OS NR for either arm). The OS rate for ibr at 3 y was 74%. ORR for ibr was 91% with CR/CRi rates (now 9%) increasing over time. Baseline cytopenias improved with extended ibr therapy for hemoglobin (85%), platelet (95%), and absolute neutrophil counts (95%). AE profile of ibr was consistent with previous reports. Major hemorrhage, Gr ≥3 atrial fibrillation, and Gr ≥3 hypertension occurred in 6%, 6%, and 8% of pts, respectively, over a follow-up of up to 4 y. Incidence of most Gr ≥3 AEs decreased from y 1 vs y 2-3: neutropenia- 18% vs 8%; pneumonia- 11% vs 4%; atrial fibrillation- 4% vs 2%, respectively. Discontinuations were most frequently PD (27%) and AE (12%). At analysis, 90 ibr pts (46%) continue ibr on study. Conclusions: Long-term treatment with ibr in this international ph III RESONATE study is tolerable and continues to show sustained PFS and OS regardless of high-risk cytogenetics. Ph III results in relapsed del17p and del11q pts compare favorably to prior ph II reports. Clinical trial information: NCT01578707