Phase II study of combining immunotherapy and pulsed low dose rate radiotherapy for abdominal metastasis of gastric cancer.

Abstract

e16099 Background: Immune-mediated responses against tumor antigens by checkpoint inhibitors (CPIs) may be enhanced by radiotherapy and the combination may hold therapeutic promise. Pulsed low dose rate radiotherapy (PLDR) is an effective strategy for abdominal tumor by taking advantage of low dose hyper-radiosensitivity with maximizing tumor response and minimizing adverse events by radiotherapy. In this phase II study, we prospectively analyzed the response and adverse events of the combination strategy of CPIs and PLDR for abdominal metastasis of gastric cancer. Methods: Eligibility criteria included pathologically confirmed advanced gastric adenocarcinoma with abdominal metastasis. Patients received XELOX regimen chemotherapy, anti-PD-1 toripalimab, and PLDR for abdominal metastasis, prescription dose was 50-56Gy/25-28f. The primary endpoint was objective response rate (ORR) and safety. Secondary endpoints were regional response rate (RRR) and regional controlled rate (RCR) for radiotherapy target tumor, progression-free survival (PFS), and overall survival (OS). Results: Between November 2018 and June 2020, 24 patients were enrolled and included in the efficacy analysis. 13 of them were first line therapy, and 11 of them were second line therapy. The ORR was 70.8% and the combination regimen were tolerable. The RRR was 83.3% and the RCR was 95.8%. The median PFS was 11.1 months and the median OS was not yet reached. Conclusions: In this phase II clinical trial, the combination of Immunotherapy and radiotherapy provided good response and toleration for abdominal metastasis of gastric cancer. It suggested clinical efficacy of this regimen in patients with advanced gastric cancer. Clinical trial information: NCT03061162.