7528 Background: Previously in the COMPLEMENT 1 study, treatment with OFA and CHL in pts with untreated CLL had shown a significant improvement in the progression-free survival (PFS) compared with CHL alone, and was well tolerated. Here, we report the final overall survival (OS) analysis of the 5-year (y) follow-up, updated investigator-assessed PFS and safety from the study. Methods: Untreated pts, not fit for fludarabine-based therapy (due to advanced age or co-morbidities) were randomized 1:1 to OFA+CHL or CHL alone. Pts in OFA+CHL arm received OFA (Cycle 1: 300 mg day (d) 1, 1000 mg d8; subsequent cycles: 1000 mg d1) in addition to CHL (10 mg/m2, d1-7) for 3 to 12 cycles of 28 d each. Pts in CHL arm received CHL only. Results: Overall, 447 pts were randomized to OFA+CHL (n = 221) or CHL (n = 226); 168 (76%) and 164 (73%) pts completed the scheduled treatments, respectively. Baseline characteristics were similar in both arms. The investigator-assessed median PFS was 23.4 months (mos) in the OFA+CHL arm and 14.7 mos in the CHL arm (HR: 0.61 [95% CI 0.49, 0.76], p < 0.001). Median OS could not be estimated for the OFA+CHL arm and was 84.7 mos for the CHL arm (HR: 0.88 [95% CI 0.65, 1.17], p = 0.363). Estimated OS rate (95% CI) at 5 y was 68.5% (61.5%, 74.5%) in the OFA+CHL arm, and 65.7% (58.6%, 71.9%) in the CHL arm. Post-treatment anti-cancer therapy after discontinuation was received by a greater proportion of pts in the CHL (66%) vs. OFA+CHL (56%), and started earlier in the CHL arm (486 d) vs. OFA+CHL (743 d) arm. Overall, 84 (39%) pts in the OFA+CHL, and 99 (44%) pts in the CHL arms died during the study with 5 on-treatment deaths in each group. Grade ≥3 adverse events were seen in 64% and 48% of pts in the OFA+CHL vs. CHL arms, respectively, most common being (≥5% in either arm) neutropenia (26% vs. 15%), thrombocytopenia (5% vs. 10%), pneumonia (9% vs. 5%), and anemia (5% vs. 5%). Conclusions: This 5-y survival follow-up analysis supported the results from primary analysis with an estimated 12% (not significant) and 39% risk reduction in OS and PFS, respectively, in the OFA+CHL arm compared with the CHL arm. No new safety concerns were observed in the OFA+CHL arm. Clinical trial information: NCT00748189.