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

Pancreatic cancer is an aggressive disease with treatment options associated with modest benefit, therefore, new treatment options are needed. Paricalcitol is a man-made form of vitamin D. It is thought to work by blocking a signal in the cancer tumor cells that leads to growth and spreading of the tumor. Paricalcitol was approved by the Food and Drug Administration (FDA) for the prevention and treatment of elevated calcium levels associated with chronic renal failure. The FDA has not approved paricalcitol as a treatment for pancreatic cancer. This research study is being performed to evaluate the benefit of paricalcitol in combination with gemcitabine and nab-paclitaxel for this disease. The FDA (the U.S. Food and Drug Administration) has approved the combination of gemcitabine and nab-paclitaxel as a treatment option for this disease. Treatment will consists of 4 week treatment cycles. Paricalcitol in the oral formulation will be taken daily, in the intravenous formulation will be administered three times a week. Nab-paclitaxel and gemcitabine will be administered on days 1,8, and 15. Subjects continue in the study until disease progression, adverse event/toxicity, death or either the subject or sponsor discontinues the study. In this research study, the main objectives include: * Assess adverse side effects associated with the combination of paricalcitol with gemcitabine and nab-paclitaxel. * Evaluate overall survival in patients with pancreatic cancer receiving gemcitabine and nab-paclitaxel with or without paricalcitol. Phase II was not pursued due to futility based on the results of the NAPOLI-3 therapeutic clinical trial.