Background: BGB-283 is a novel inhibitor of the RAF dimer with potent and reversible inhibitory activities against RAF family kinases including wild type A-RAF, B-RAF, C-RAF and B-RAF V600E, as well as EGFR. BGB-283 demonstrated acceptable safety and early clinical activity in its Phase 1A study. In this Phase IB dose expansion study, we further evaluated safety and tolerability of BGB-283 and investigated efficacy in pre-selected patients (pts) with B-RAF or K-RAS/N-RAS-mutated solid tumors. Methods: This Phase 1B study was a multicenter, open-label, multiple-arm, dose expansion study. Pts were treated at the RP2D of BGB-283 at 30 mg/day. There were 10 different expansion arms for: B-RAF V600-mutated melanoma (not previously treated with a B-RAF or MEK inhibitor, and B-RAF and/or MEK inhibitor-resistant pts), colorectal cancer (CRC), non-small cell lung cancer (NSCLC), papillary thyroid cancer (PTC) and other solid tumors with B-RAF mutations; K-RAS/N-RAS-mutated endometrial cancer, NSCLC, CRC, and other solid tumors with K-RAS/N-RAS or NF-1 mutations. The primary end point was the response rate based on RECIST Version 1.1. Adverse events (AEs) are reported per CTCAE V4.03. Results: As of 19th Sep 2016, 96 pts were enrolled: median age was 63 years (range: 20 to 82 years) with all pts having baseline ECOG PS of 0 or 1. Forty-seven (49.0%) subjects had received ≥3 prior lines of treatment, 22 (22.9%) had received 2 prior lines of treatment, and 18 (18.8%) had received 1 prior line of treatment. BGB-283 was generally well-tolerated. Drug-related AEs were mostly Grade 1/2 in severity; the most common were fatigue in 37 (38.5%) subjects, nausea in 16 (16.7%), decreased appetite in 21 (21.9%), and diarrhea in 17 (17.7%). A total of 34 (35.4%) subjects experienced study drug-related Grade 3/4 AEs, notably drug-related thrombocytopenia (6.3%), palmar-plantar erythrodysesthesia syndrome (1.0%) and hypertension (8.3%). In the cohorts with previously-untreated B-RAF V600-mutated melanoma (n=7), PTC with B-RAF mutation (n=3) and NSCLC with K-RAS mutation (n=6), the response rates were 42.9% (95% confidence interval [CI], 9.9, 81.6), 33.3% (95% CI, 0.8, 90.6) and 16.7% (95% [0.4, 64.1]), respectively. Confirmed PR was seen in the single case of ovarian cancer with B-RAF mutation enrolled and also in one of 4 melanoma subjects with a confirmed B-RAF V600 mutation, who had not responded to B-RAF and/or MEK inhibitor(s). One unconfirmed PR was found in two NSCLC subjects with a B-RAF mutation. Conclusions: BGB-283 was generally well-tolerated during the Phase 1B stage of the study. Antitumor activity was not only observed in subjects with B-RAF V600-mutated solid tumors including melanoma, PTC, and ovarian cancer, but also in subjects with K-RAS-mutated NSCLC. When added to the efficacy data in the Phase IA portion of this study, with objective responses noted in these tumor subtypes as well as in K-RAS-mutated endometrial carcinoma, BGB-283 demonstrated a desirable risk-benefit profile for further efficacy and safety investigation.

Citation Format: Jayesh Desai, Hui Gan, Catherine Barrow, Michael B. Jameson, Ben Solomon, Victoria Atkinson, Andrew Haydon, Michael Millward, Stephen Begbie, Michael Brown, Benjamin Markman, William Patterson, Andrew Hill, Lisa Horvath, Adnan Nagrial, Gary Richardson, Christopher Jackson, Michael Friedlander, David Gibbs, Phillip Parente, Jason Yang, Lai Wang, Yunxin Chen, Lusong Luo. A Phase IB study of RAF dimer inhibitor BGB-283 in patients with B-RAF or K-RAS/N-RAS mutated solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr CT002. doi:10.1158/1538-7445.AM2017-CT002