Preliminary results of BEAVER: An investigator-initiated phase II study of binimetinib and encorafenib for the treatment of advanced solid tumors with non-V600E BRAF mutations (mts).

Abstract

e15038 Background: Recurring oncogenic non-V600E BRAF mts have been identified in many cancer types. Preclinical data indicate that some BRAF non-V600E mts can be targeted with BRAF + MEK inhibitors. BEAVER is an investigator-initiated study designed to test the safety and efficacy of binimetinib and encorafenib (B+E) in patients (pts) with non-V600E BRAF mts. Methods: Key eligibility criteria are: pts with advanced solid tumors with BRAF non-V600E activating (class 1 and 2) or inhibitory (class 3) mts, and no prior BRAF/MEK inhibitors. Pts receive binimetinib (45mg PO BID) and encorafenib (450mg PO daily) on a 28-day cycle until intolerable toxicity or progression. The primary objective is OR rate (ORR) as per RECIST 1.1. In this Simon 2-stage trial, ≥1 of 7 pts need to have an objective response (OR) before commencing second stage of study (26 pts total). Secondary objectives include: safety, DCR, PFS, and OS. Exploratory objectives include: genomic profiling of tumors, evaluating circulating tumor DNA dynamics and development of patient derived xenograft (PDX) models. Results: From June 2019 to Feb 2021, 12 pts were screened and 9 pts enrolled; 9 are evaluable for safety and 8 for efficacy. Tumor types were melanoma and colon (n=2 each), as well as gallbladder, lung, breast and uterine cancers (n=1 each). Median age was 62 yrs (range 40-72). Median number of prior treatments was 2 (range 0-6). 1 pt had a class 1, 3 pts had class 2, and 5 pts had class 3, non-V600E BRAF mts. The median number of cycles was 2 (range: 1-7). Common treatment-related adverse events were mostly grade ≤ 2, and included: Blurred vision (78%), fatigue (67%), nausea (44%), vomiting (33%), and rash (33%). Dose reductions were required in 4/9 pts (44%) due to: blurred vision (22%), central serous retinopathy (11%), malaise (11%) and increased lipase (11%). Drug-related grade 3 AEs occurred in 2/9 pts and included: malaise (11%), confusion (11%), fatigue (11%) and increased lipase (11%). All eye toxicities were reversible with dose interruption. ORR was 12.5% (1/8) with one unconfirmed PR in a melanoma pt (BRAF G469S), treated for 6.5 months. One gallbladder cancer pt (BRAF D594N) had SD, and 6 pts had PD as best response. Genomic profiling was performed on archival tumors for 8 pts. Two PDX models were established. Responses to B+E in PDX models mirrored responses in 2 corresponding pts who had PD. Genomic and molecular profiling of pt tumors and corresponding PDXs identified multiple potential mechanisms of B+E resistance including: activation of EGFR and Akt pathways and inactivation of NF1 and Rb1. Conclusions: Preliminary data confirmed the safety of B+E and showed preliminary evidence of anti-tumor activity in advanced cancer pts with non-V600E BRAF mts. This study met the criterion for advancing to stage 2. Enrolment in the BEAVER trial and correlative biomarker analyses are ongoing. Clinical trial information: NCT03839342.