Paricalcitol Plus Gemcitabine and Nab-paclitaxel in Metastatic Pancreatic Cancer

This research study is a two stage study which consists of a safety run-in phase and a randomized phase 2 study which include subjects with previously-untreated, metastatic pancreatic adenocarcinoma. In the run-in safety study, the safety of adding two formulations (IV or Oral) of paricalcitol to a standard chemotherapy program of gemcitabine and nab-paclitaxel will be evaluated. The randomized phase 2 study will evaluate the efficacy of paricalcitol when added to gemcitabine and nab-paclitaxel The drugs involved in this study are: * Paricalcitol * Gemcitabine * Nab-paclitaxel