Background: First-line cytotoxic chemotherapy improves survival for patients with metastatic pancreatic adenocarcinoma (PDA) but the majority will progress after a median of 5-7 months. CD8 T-cells are thought to be the major anti-tumor effector cells and their density in resected pancreatic tumors correlates with survival. Our published pre-clinical data in the KPC-Brca1 mouse model shows that treatment with a hypomethylating agent inhibits tumor growth (Shakya, Gonda et al., Cancer Res, 2013) and, in recent data (B.T. and T.G. in preparation), combining a hypomethylating agent with an immune checkpoint inhibitor leads to slowing of tumor growth and increased survival in KPC mice. We propose a novel approach to improve response rates with immune checkpoint blockade in pancreatic cancer by utilizing a hypomethylating agent to prime the tumor and its microenvironment, thereby increasing the number of intratumoral effector T cells, decreasing the immunosuppressive cell population, and influencing stromal-tumor cell interactions. Methods: Thirty-one evaluable subjects with advanced pancreatic cancer will be enrolled in this phase II study to evaluate the efficacy and safety of pembrolizumab following induction with azacitidine in the second-line setting. All subjects will have received a single line of chemotherapy for locally advanced or metastatic PDA prior to study enrollment. Subjects must have available baseline biopsy or archival tissue for analysis. Low-dose azacitidine (50 mg/m2 subcutaneous) will be given daily for 5 days every 4 weeks, and pembrolizumab 200 mg IV will be administered starting on day 15 and then continued every 3 weeks. Subjects will undergo an on-treatment biopsy during week 8. The primary efficacy endpoint will be PFS according to RECIST v1.1 criteria. There will be an accelerated phase Ib dose determination component with an initial 6 subjects. Secondary endpoints will include safety/tolerability, ORR, DOR, and OS. Multiple correlative analyses utilizing tissue and serum samples will be performed. Clinical trial information: NCT03264404