Purpose: The effectiveness of immune checkpoint inhibitors (ICI) is limited in pancreatic ductal adenocarcinoma (PDAC). We conducted a phase I study to evaluate the safety of ICI with stereotactic body radiation therapy (SBRT) in patients with metastatic PDAC. Patients and Methods: Patients enrolled must have received at least one line of prior systemic chemotherapy for metastatic disease. Cohorts A1 and A2 received durvalumab every 2 weeks plus either 8 Gy in one fraction of SBRT on day 1 or 25 Gy in five fractions on day −3 to +1. Cohorts B1 and B2 received durvalumab plus tremelimumab every 4 weeks and either 8 Gy in one fraction of SBRT on day 1 or 25 Gy in five fractions on day −3 to +1. ICIs were continued until unacceptable toxicity or disease progression. The primary objective was the safety and feasibility of treatment. Objective response was assessed in lesions not subjected to SBRT. Results: Fifty-nine patients were enrolled and 39 were evaluable for efficacy. No dose-limiting toxicities were seen. The most common adverse event was lymphopenia. Two patients achieved a partial response (one confirmed and the other unconfirmed). The overall response rate was 5.1%. Median PFS and OS was 1.7 months [95% confidence intervals (CI), 0.8–2.0 months] and 3.3 months (95% CI, 1.2–6.6 months) in cohort A1; 2.5 months (95% CI, 0.1–3.7 months) and 9.0 months (95% CI, 0.5–18.4 months) in A2; 0.9 months (95% CI, 0.7–2.1 months) and 2.1 months (95% CI, 1.1–4.3 months) in B1; and 2.3 months (95% CI, 1.9–3.4 months) and 4.2 months (95% CI, 2.9–9.3 months) in B2. Conclusions: The combination of ICI and SBRT has an acceptable safety profile and demonstrates a modest treatment benefit in patients with metastatic PDAC.
