S146: VENETOCLAX IN PATIENTS WITH CHRONIC LYMPHOCYTIC LEUKEMIA WITH 17P DELETION: 6-YEAR FOLLOW-UP AND GENOMIC ANALYSES IN A PIVOTAL PHASE 2 TRIAL

Abstract

Background: Patients (pts) with chronic lymphocytic leukemia (CLL) with del(17p) and/or mutated TP53 have adverse prognosis and are a population of interest for improving outcomes. In a pivotal Phase 2 study (NCT01889186) evaluating venetoclax (Ven; a selective oral BCL2 inhibitor) monotherapy in del(17p) CLL (N=158), overall response rate (ORR) was 77% (median time on study, 26.6 mo; Stilgenbauer. J Clin Oncol. 2018;17:1973). Aims: To report final analyses after 5 y from last pt enrolled, including post-hoc subgroup analyses of prognostic markers. Methods: Adults with R/R or previously untreated del(17p) CLL received Ven 400 mg (via ramp-up) orally daily until progressive disease (PD) or intolerance. Main cohort comprised pts with R/R CLL; safety expansion cohort included pts with R/R or untreated CLL. Primary endpoints were ORR (main) and safety (safety expansion). Peripheral blood (PB) and bone marrow (BM) were analyzed pre-Ven for somatic mutations via targeted next-generation sequencing (NGS). Minimal residual disease (MRD) was assessed by flow cytometry, ASO-PCR, and/or clonoSEQ NGS; undetectable MRD (uMRD) is reported at <10−4. Results: In all, 158 pts received Ven (main, n=107; safety expansion, n=51). Data cutoff was 15 December 2020. Pts had median 2 (range, 0−10) prior lines of therapy (LOT); 5 had untreated CLL (first-line [1L]). Common mutations (n/N) were TP53 (113/138 [82%]; 35/113 [31%] had >1), SF3B1 (28/137 [20%]) NOTCH1 (22/137 [16%]), ATM (11/120 [9%]), and BIRC3 (6/120 [5%]); 93/115 (81%) had unmutated IGHV and 118/158 (75%) had ≥20% del(17p). Median time on Ven was 27.4 (range, 0–79.3) mo. At study close, 77 pts were alive; 26 remained on Ven. No new safety signals were observed. With 70 mo median follow-up (f/u), investigator-assessed ORR was 77% (95% CI, 70−84); 21% achieved complete remission (CR)/CR with incomplete blood count recovery (CRi). Median duration of response was 39.3 mo (95% CI, 31.1−50.5); 28% had ongoing response at 60 mo. Of 61 evaluable pts with a PB MRD assessment, 25% had uMRD at ~2 y (24−30 mo). Median progression-free survival (mPFS) was 28.2 mo (95% CI, 23.4−37.6; Figure). Median overall survival (mOS) was 62.5 mo (95% CI, 51.7−NR; 5-y PFS and OS rates, 24% and 52%). Of 5 1L pts, 4 were alive and progression-free. In pts with CR/CRi (n=37), mPFS was 62.2 mo (95% CI, 53.1−NR); in pts with partial remission (PR)/nodular PR (n=85), mPFS was 27.6 mo (95% CI, 22.8−38.0). Overall, 98/158 (62%) pts had PD, including 24/158 (15%) with Richter transformation. Of pts with PD (n=98) or whose disease was refractory to Ven (n=11), 73 received another LOT, most commonly ibrutinib (n=41); mOS from ibrutinib initiation was 28.0 mo. In pts with both del(17p) and TP53 mutation (n=111) vs those with either (n=19), ORR was 75% vs 79%; mPFS was 27.4 vs 22.8 mo (P=.8). In pts with mutated (n=22) vs unmutated IGHV (n=93), mPFS was 40.4 vs 26.9 mo (P=.11). No significant difference in ORR, PFS, or OS was observed in pts with vs without ≥20% del(17p), >1 TP53 mutation, NOTCH1, ATM, or BIRC3 mutations; mPFS was shorter in pts with mutated SF3B1 (n=28) vs without (n=109; 16.4 vs 30.2 mo [P=.0071]). Multivariate analysis is ongoing. Image:Summary/Conclusion: At end of study (median f/u, 70 mo), 48% of pts were alive, 24% were progression-free, and 16% remained on Ven, confirming the long-term activity of Ven in this high-risk population with del(17p) CLL and median 2 prior LOT. Except SF3B1 mutation, other adverse features (eg, >1 TP53 mutation, NOTCH1 mutations, unmutated IGHV) did not influence outcomes with Ven treatment in this cohort.