Short-course radiation followed by mFOLFOX-6 plus avelumab for locally advanced rectal adenocarcinoma.

139 Background: Total neoadjuvant treatment (TNT) for locally advanced rectal cancer is becoming an accepted approach over the last few years with increasing pathologic complete response (pCR) and compliance of patients for chemotherapy in comparison with the current standard of care i.e., fluoropyrimidine based chemoradiation followed by surgery and adjuvant chemotherapy. Sequential use checkpoint inhibitors after radiation therapy (RT) has demonstrated synergistic effect in vivo leading to decrease in size of irradiated and non-irradiated secondary tumors outside the radiation field (abscopal effect). Methods: This is an investigator initiated; open-label, single-arm multicenter phase II study, adopting Simon’s two-stage aiming at evaluating the pCR rate and safety of using short-course radiation therapy (25 Grays in 5 fractions), followed by 6 cycles of mFOLFOX-6 plus Avelumab (anti PDL1), then total mesorectal excision(TME) in patients with locally-advanced, potentially resectable rectal adenocarcinoma. Results: 13 out of 44 patients were accrued from 20, July till 28, Dec 2018 in the first stage of the study (30% from total sample size). They all met the inclusion criteria and received full protocol treatment. 12 out of the 13 completed TME. 1 of the 13 had progression of disease, so surgery was aborted and patient was dropped out the study. The sample consisted of 9 (69%) males and 4 (31%) females with median age of 62 (33.0, 73.0) years. The first interim analysis revealed 3 patients (25%) achieved pCR (tumor regression grade: TRG = 0) out of 12 as compared to the historical control group with pCR of 16%. For the rest of the patients, 3 (25%) had major pathologic response rate (pRR) with TRG = 1 (< 10% viable cells is tumor bed).In total, 6 out of 12 patients (50%) had major pathologic response rate. As for safety, no serious adverse events of grade 3 and 4 were reported. Conclusions: Based on the first interim analysis results, incorporation of Avelumab and short course radiotherapy is tolerable in patients with locally advanced rectal cancer treated with TNT. The study will resume recruitment to reach the target accrual. Clinical trial information: NCT03503630.