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In the primary analysis report of the GAIA/CLL13 trial, we found that venetoclax–obinutuzumab and venetoclax–obinutuzumab–ibrutinib improved undetectable measurable residual disease (MRD) rates and progression-free survival compared with chemoimmunotherapy in patients with previously untreated chronic lymphocytic leukaemia. However, to our knowledge, no data on direct comparisons of different venetoclax-based combinations are available. GAIA/CLL13 is an open-label, randomised, phase 3 study conducted at 159 sites in ten countries in Europe and the Middle East. Eligible patients were aged 18 years or older, with a life expectancy of at least 6 months, an Eastern Cooperative Oncology group performance status of 0–2, a cumulative illness rating scale score of 6 or lower or a single score of 4 or lower, and no TP53 aberrations. Patients were randomly assigned (1:1:1:1), with a computer-generated list stratified by age, Binet stage, and regional study group, to either chemoimmunotherapy, venetoclax–rituximab, venetoclax–obinutuzumab, or venetoclax–obinutuzumab–ibrutinib. All treatments were administered in 28-day cycles. Patients in the chemoimmunotherapy group received six cycles of treatment, with patients older than 65 years receiving intravenous bendamustine (90 mg/m2, days 1–2), whereas patients aged 65 years or younger received intravenous fludarabine (25 mg/m2, days 1–3) and intravenous cyclophosphamide (250 mg/m2, days 1–3). Intravenous rituximab (375 mg/m2, day 1 of cycle 1; 500 mg/m2, day 1 of cycles 2–6) was added to chemotherapy. In the experimental groups, patients received daily venetoclax (400 mg orally) for ten cycles after a 5-week ramp-up phase starting on day 22 of cycle 1. In the venetoclax–rituximab group, intravenous rituximab (375 mg/m2, day 1 of cycle 1; 500 mg/m2, day 1 of cycles 2–6) was added. In the obinutuzumab-containing groups, obinutuzumab was added (cycle 1: 100 mg on day 1, 900 mg on day 2, and 1000 mg on days 8 and 15; cycles 2–6: 1000 mg on day 1). In the venetoclax–obinutuzumab–ibrutinib group, daily ibrutinib (420 mg orally, from day 1 of cycle 1) was added until undetectable MRD was reached in two consecutive measurements (3 months apart) or until cycle 36. The planned treatment duration was six cycles in the chemoimmunotherapy group, 12 cycles in the venetoclax–rituximab and the venetoclax–obinutuzumab group and between 12 and 36 cycles in the venetoclax–obinutuzumab–ibrutinib group. Coprimary endpoints were the undetectable MRD rate in peripheral blood at month 15 for the comparison of venetoclax-obinutuzumab versus standard chemoimmunotherapy and investigator-assessed progression-free survival for the comparison of venetoclax-obinutuzumab-ibrutinib versus standard chemoimmunotherapy, both analysed in the intention-to-treat population (ie, all patients randomly assigned to treatment) with a split α of 0·025 for each coprimary endpoint. Both coprimary endpoints have been reported elsewhere. Here we report a post-hoc exploratory analysis of updated progression-free survival results after a 4-year follow-up of our study population. Safety analyses included all patients who received at least one dose of study treatment. This study is registered with ClinicalTrials.gov , NCT02950051 , recruitment is complete, and all patients are off study treatment. Between Dec 13, 2016, and Oct 13, 2019, 1080 patients were screened and 926 were randomly assigned to treatment (chemoimmunotherapy group n=229; venetoclax–rituximab group n=237; venetoclax–obinutuzumab group n=229; and venetoclax–obinutuzumab–ibrutinib group n=231); mean age 60·8 years (SD 10·2), 259 (28%) of 926 patients were female, and 667 (72%) were male (data on race and ethnicity are not reported). At data cutoff for this exploratory follow-up analysis (Jan 31, 2023; median follow-up 50·7 months [IQR 44·6–57·9]), patients in the venetoclax–obinutuzumab group had significantly longer progression-free survival than those in the chemoimmunotherapy group (hazard ratio [HR] 0·47 [97·5% CI 0·32–0·69], p<0·0001) and the venetoclax–rituximab group (0·57 [0·38–0·84], p=0·0011). The venetoclax–obinutuzumab–ibrutinib group also had a significantly longer progression-free survival than the chemoimmunotherapy group (0·30 [0·19–0·47]; p<0·0001) and the venetoclax–rituximab group (0·38 [0·24–0·59]; p<0·0001). There was no difference in progression-free survival between the venetoclax–obinutuzumab–ibrutinib and venetoclax–obinutuzumab groups (0·63 [0·39–1·02]; p=0·031), and the proportional hazards assumption was not met for the comparison between the venetoclax–rituximab group versus the chemoimmunotherapy group (log-rank p=0·10). The estimated 4-year progression-free survival rate was 85·5% (97·5% CI 79·9–91·1; 37 [16%] events) in the venetoclax–obinutuzumab–ibrutinib group, 81·8% (75·8–87·8; 55 [24%] events) in the venetoclax–obinutuzumab group, 70·1% (63·0–77·3; 84 [35%] events) in the venetoclax–rituximab group, and 62·0% (54·4–69·7; 90 [39%] events) in the chemoimmunotherapy group. The most common grade 3 or worse treatment-related adverse event was neutropenia (114 [53%] of 216 patients in the chemoimmunotherapy group, 109 [46%] of 237 in the venetoclax–rituximab group, 127 [56%] of 228 in the venetoclax–obinutuzumab group, and 112 [48%] of 231 in the venetoclax–obinutuzumab–ibrutinib group). Deaths determined to be associated with study treatment by the investigator occurred in three (1%) patients in the chemoimmunotherapy group (n=1 due to each of sepsis, metastatic squamous cell carcinoma, and Richter's syndrome), none in the venetoclax–rituximab and venetoclax–obinutuzumab groups, and four (2%) in the venetoclax–obinutuzumab–ibrutinib group (n=1 due to each of acute myeloid leukaemia, fungal encephalitis, small-cell lung cancer, and toxic leukoencephalopathy). With more than 4 years of follow-up, venetoclax–obinutuzumab and venetoclax–obinutuzumab–ibrutinib significantly extended progression-free survival compared with both chemoimmunotherapy and venetoclax–rituximab in previously untreated, fit patients with chronic lymphocytic leukaemia, thereby supporting their use and further evaluation in this patient group, while still considering the higher toxicities observed with the triple combination. AbbVie, Janssen, and F Hoffmann-La Roche. [ABSTRACT FROM AUTHOR]