 Gemcitabine and nab-paclitaxel is a standard regimen NCCN, Category 1 for patients with metastatic pancreatic ductal adenocarcinoma PDAC. However, further improvement in treatment is needed. Increasingly, the nature of the immune infiltrate in PDAC appears to be tumor promoting. In preclinical studies, ibrutinib treatment, presumably by reprogramming B cells, results in increased CD8 T cells to assist in tumor control. Preclinical studies of ibrutinib plus gemcitabine show superior antitumor effects compared to gemcitabine alone in both orthotopic murine pancreatic cancer cell line grafts and in genetically engineered mouse models. Thus, the investigators propose a clinical trial of ibrutinib plus the standard gemcitabine based regimen of gemcitabine and nab-paclitaxel, evaluating safety, then efficacy and including correlative studies. 