The purpose of this study is to determine the effectiveness of combining immune therapy, pembrolizumab, with a hypomethylating agent, azacitidine, for pancreatic cancer. People who have advanced pancreatic cancer with disease progression on first-line therapy are usually treated with a second chemotherapy regimen. However, there is no single accepted chemotherapy regimen and national guidelines recommend chemotherapy or clinical trial participation. In this study, all study subjects will receive a combination of immune therapy (every 3 weeks) and a hypomethylating agent (every 4 weeks). To date, studies have shown that combining a hypomethylating agent with chemotherapy or immune therapy may benefit patients across different solid tumor types including pancreatic cancer. Preclinical data in a mouse model of pancreatic cancer demonstrates improvement in survival with the combination of a hypomethylating agent and immune therapy. However, the use of single agent hypomethylating agent or immune therapy has not been shown to be effective in patients with pancreatic cancer. The one exception, to date, is the use of immune therapy in those individuals with a particular genetic feature known as mismatch repair deficiency and microsatellite instability. The combination of immune therapy and a hypomethylating agent has not been studied in human subjects and is not approved by the FDA for use in pancreatic cancer.

This is a non-randomized, single-center, open-label trial of pembrolizumab and azacitidine in subjects with locally advanced or metastatic pancreatic adenocarcinoma. Approximately 31 individuals will be asked to participate in this study.

Pancreatic ductal adenocarcinoma (PDA) has the worst prognosis of any major malignancy in the United States and, unlike other common cancers, annual deaths from PDA are rising. Despite recent advances, cytotoxic chemotherapy for PDA has been disappointing. Even among the small subset of patients who are suitable for surgical resection at the time of diagnosis, complete resection is followed by recurrence in majority of patients without further systemic therapy. Thus all PDA patients require systemic chemotherapy and more effective regimens are urgently needed.

Combination chemotherapy is effective in controlling disease and prolonging survival in patients with advanced pancreatic cancer. Despite recent successful phase 3 studies in the first-line setting, there is no defined second-line treatment for patients who experience disease progression following first-line therapy. Consensus guidelines (such as the National Comprehensive Cancer Network (NCCN) guidelines) recommend clinical trial participation in this setting.

The investigators' pre-clinical data suggests that decitabine treatment in the KPC model of pancreatic cancer leads to a significant up-regulation of interferon-related genes and a polarization of the infiltrating immune cells. Based on these results, the investigators have evaluated the effect of single agent decitabine or anti-PD1H (a homologue of PD1 with very similar function and expression pattern) compared to combination therapy (treatment with decitabine followed by PD1H blockade). The investigators' preliminary results showed minimal effect of either agent alone on tumor growth but marked decrease in tumor progression in the combination arm. These results form the foundation of this phase II study.

This study will treat patients with the combination of azacitidine and pembrolizumab. A direct comparison between azacitidine and decitabine in terms of efficacy within a controlled clinical trial has not been performed thus far. In randomized myelodysplastic syndrome (MDS) trials, the remission rates were similar for azacitidine and decitabine but the overall survival in the experimental arm was significantly shorter in the decitabine trial compared to the azacitidine trial. A primary reason to utilize azacitidine in this setting is our desire to amply reduced dose therapy with the goal of maintaining subjects on therapy Low-dose azacitidine is being tested in phase I/II clinical trials for advanced solid tumors-mainly colorectal cancer, small-cell lung carcinomas, ovarian cancer, and breast cancer.

Inclusion Criteria:

• Be willing and able to provide written informed consent for the trial.
• Age ≥18 years of age on day of signing informed consent.
• Have confirmed diagnosis of pancreatic ductal adenocarcinoma
• Have a predicted life expectancy of greater than 3 months.
• Have measurable disease based on RECIST 1.1.
• Have a performance status of 0 or 1 using the Eastern Cooperative Oncology Group (ECOG) Performance Scale within 3 days of first dose of study drug.
• Have documented radiographic progression to or documented intolerance of first line systemic chemotherapy which included either gemcitabine or Fluorouracil (5-FU) based regimen (including capecitabine).
• Subjects who have documented disease recurrence within 6 months of completing neoadjuvant or adjuvant chemotherapy for limited disease will be eligible for study. Subjects who recur greater than 6 months after completing adjuvant or neoadjuvant chemotherapy will not be eligible unless they receive additional chemotherapy for advanced disease.

Exclusion Criteria:

• Is currently participating and receiving study therapy or has participated in a study of an investigational agent and received study therapy, or herbal/complementary oral or IV medicine within 2 weeks of the first dose of treatment.
• Has received chemotherapy or radiotherapy within 14 days of first dose of study medication.

Throughout study duration, up to approx 80 months