A phase II study of ipilimumab and nivolumab with radiation in metastatic pancreatic adenocarcinoma.

391 Background: Pancreatic ductal adenocarcinoma (PDAC) remains a highly lethal cancer. Immunotherapy (IO) has shown minimal activity. In preclinical models, radiation (XRT) increases likelihood of response to IO via an abscopal effect where local tx (treatment) of a tumor leads to an antitumor response distantly, with synergy between XRT and dual checkpoint blockade. In this study, we assessed CTLA-4 and PD-1 blockade with XRT as a strategy to stimulate an immune response for patients (pts) with PDAC. Methods: In this open-label, single arm phase-2 study, we enrolled 25 metastatic PDAC pts in an exploratory cohort. Eligible pts had histologically-confirmed PDAC, ECOG PS 0-1, and progression on at least 1 line of tx. Tx consisted of Ipilimumab (1 mg/kg every 6 wks), Nivolumab (240 mg every 2 wks) and 3 fractions of 8 Gy of XRT at cycle 2. Tx continued until PD, discontinuation or withdrawal. Endpoints include Disease Control Rate (DCR), ORR, PFS, OS and safety. Radiological evaluations were every 3 months. Response was defined as disease control outside of the radiation field. We obtained serial tumor biopsies pre-tx, during checkpoint blockade alone and 2 weeks after XRT. Intention to treat analysis includes all pts receiving at least one dose of study tx. Results: 22 pts were enrolled and evaluable from 6/2017-6/2018, median age 60 years (32-75), 73% male and 100% MSS. DCR was 27% and ORR was 14% with 1 pt having a complete response. All responses were out of the radiation field. Median PFS was 76 days in the entire cohort; 163 days for pts with disease control vs 62.5 days for pts with PD or who came off study prior to initial imaging. 7 pts did not receive XRT due to clinical progression. Treatment-related adverse events (AEs) were reported in 12/22 pts (54.5%). 8/22 pts (36.4%) experienced grade ≥ 3 toxicities. Elevated lipase, lymphopenia, fatigue, hyperglycemia, mucositis and hepatitis were the most common AEs. 1/22 (4.5%) pt had a grade 5 AE possibly related to tx. Conclusions: Dual blockade of CTLA-4 and PD-1 with XRT is feasible and demonstrates promising activity in pts with metastatic PDAC. We will report the updated efficacy and safety data as well as outcomes from the correlative serial biopsies upon completion. Clinical trial information: NCT03104439.