S145: THE COMBINATION OF IBRUTINIB PLUS VENETOCLAX RESULTS IN A HIGH RATE OF MRD NEGATIVITY IN PREVIOUSLY UNTREATED CLL: THE RESULTS OF THE PLANNED INTERIM ANALYSIS OF THE PHASE III NCRI FLAIR TRIAL

Abstract

Background: Ibrutinib (I) and venetoclax (V) improve outcome in CLL. I rarely eradicates measurable residual disease (MRD), whereas V (alone or with anti-CD20) can eradicate MRD permitting time limited therapy. Small studies suggest synergy between I and V, as I+V results in MRD negativity in many patients (pts). Aims: The primary aim was to compare the MRD eradication rate between I and I+V. Key secondary aims were IWCLL overall (ORR), complete response (CR) and safety. Methods: FLAIR (ISRCTN01844152), a phase III, randomised, controlled trial for previously untreated CLL requiring therapy by IWCLL criteria. Pts >75 yrs or with >20% 17p del were excluded. FLAIR was adapted in July 2017 to add two arms, I monotherapy and I+V. I was given at 420mg/day. For I+V, V was added after two months of I with dose escalation to 400mg/day over 5 weeks. The duration of therapy (DOT) was defined by MRD with treatment for up to 6 years. MRD was assessed centrally by flow cytometry, MRD negativity was defined as <1 CLL cell in 10,000 leucocytes (IWCLL criteria), was assessed in peripheral blood (PB) and bone marrow (BM) at 9 months post-randomisation, in PB at 12 months and then 6 monthly. When PB was MRD negative, this was repeated after 3 months and then in both PB & BM 3 months later. If PB & BM were negative the time to MRD negativity was calculated (treatment start to first MRD negative PB) and DOT was twice this. The earliest therapy could stop was 2 years post-randomisation. A formal interim analysis was performed when 50% pts in I and I+V arms had reached 2 yrs post-randomisation and a p-value of <0.005 was statistically significant. Results: 523 pts were randomised to I or I+V. We report the interim analysis in the first 274 pts (I [n=138] and I+V [n=136]) reaching 2 yrs post-randomisation from 83 UK Centres from 13/07/17 to 15/03/19. 72.3% male, median age 63 yrs (34.3% >65yo) and 40.9% Binet C. IGHV were available for 256 (93.4%) pts - 48.2% IGHV unmutated (≥98% homology to germline), 45.3% IGHV mutated and 9.1% Subset 2. Hierarchical FISH testing revealed 16.1% 11q del, 19% trisomy 12, 21.9% normal and 36.9% 13q del with 6.2% failed. The arms were well-balanced for all variables. For I+V arm, MRD negativity was achieved within 24 months in BM in 89/136 (65.4%) and PB in 97/136 (71.3%) compared to no pts for I (p<0.0001). MRD negativity for I+V in BM within 24 months was 51/64 (79.7%) for IGHV unmutated and 31/55 (56.4%) for IGHV mutated. At 9 months post-randomisation 49/136 (36%) I+V pts were MRD negative in BM and 56/136 (41.2%) negative in PB compared to 0/138 with I (p<0.0001). ORR at 9 months in 120/136 (88.2%) I+V pts and 119/138 (86.2%) I pts (p=0.6157). At 9 months CR in 81/136 (59.6%) for I+V and 11/138 (8%) for I (p<0.0001). For I+V CR at any time was 93.4%. At 24 months, 54/136 (39.7%) stopped I+V due to meeting MRD stopping criteria. SAEs were reported in 41.5% I+V and 38.2% I pts. Infectious SAEs 14.8% vs 19.9% and cardiac SAEs 11.9% vs 8.1% of pts for I+V & I respectively. Laboratory TLS was reported in 6/136 (4.4%) of I+V pts and none with I. There were no cases of clinical TLS. Most frequent any grade AEs within 12 months of randomisation differing between I+V & I were diarrhoea (52.6% I+V pts, 29.4% I), anaemia (28.9% vs 16.9%), leucopenia (36.3% vs 8.8%), thrombocytopenia (23.7% vs 14%). Leucopenia was the only grade ≥3 SAE reported in >10% of pts (27.4% I+V and 5.1% I). Image:Summary/Conclusion: Ibrutinib plus venetoclax is an effective and well tolerated combination resulting in a high rate of MRD negativity in blood (71.9%) and marrow (65.4%) in the first 2 years of treatment.