Regomune: A phase II study of regorafenib plus avelumab in solid tumors-Results of the biliary tract cancer (BTC) cohort.

4096 Background: Regorafenib (R) has shown promising efficacy in patients (pts) with BTC refractory to standard chemotherapy. Anti-PD1/PD-L1 antibodies have only limited clinical activity. Synergy between R and anti–PD-1/PD-L1 antibodies has been shown in pre-clinical solid tumor models. Methods: This is a single-arm open-label multicentric phase II trial (Bayesian adaptive design) assessing the efficacy and safety of R (160 mg QD 3weeks/4) + avelumab (A) (10 mg/kg every 2 weeks) combination in BTC pts. The primary endpoint was the objective response rate under treatment, based on central review according to RECIST 1.1. Secondary endpoints included: 1-year progression free survival (PFS), 1-year overall survival (OS), and Safety using NCI-CTCAE v5.0. Correlative studies were planned from pts tumor samples obtained at baseline. Results: Between Nov. 2018 and Nov. 2019, 34 BTC pts were enrolled in 4 centers. Median age was 63 (range 36 – 80). Median follow-up was 9.8 months. Median number of previous treatment lines for metastatic or locally advanced disease was: 2 (range 1 – 4). Twenty-nine (85.3%) pts experienced at least 1 dose modification or treatment interruption of R or A due to an adverse event (AE) related to the treatment. The most common grade 3/4 AEs were : Hypertension (17.6%), Fatigue (14.7%), and maculo-papular rash (11.8%). No death was related to the treatment. Among the 29 pts with at least one imaging tumor assessment, 4 (13.8%) achieved a partial response, and 11 (37.9%) demonstrated stable disease including 10 (34.5%) pts with tumor shrinkage. Fourteen pts (48.3%) had progressive disease. The median PFS and OS were 2.5 months (95%CI 1.9 – 5.5) and 11.9 months (95%CI 6.2 – NA) respectively. Baseline tumor samples were available for 27 pts. High IDO and PD-L1 expression at baseline was associated with better outcome. Conclusions: The R+A combination is associated with significant anti-tumor activity with promising survival rates in this heavily pre-treated population. Full Biomarkers analyses will be presented at the meeting. Clinical trial information: NCT03475953.