Stage IV Ampulla of Vater Cancer AJCC v8

This phase II trial tests how well giving gemcitabine, cisplatin and durvalumab alternating with pemigatinib for the treatment of biliary tract cancer with FGFR2 alterations that cannot be removed by surgery (unresectable), that has spread to nearby tissue or lymph nodes (locally advanced) or that has spread from where it first started (primary site) to other places in the body (metastatic). Gemcitabine is a chemotherapy drug that blocks the cells from making DNA and may kill cancer cells. Cisplatin is in a class of medications known as platinum-containing compounds. It works by killing, stopping or slowing the growth of cancer cells. Immunotherapy with monoclonal antibodies, such as durvalumab, may help the body's immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread. Pemigatinib is in a class of medications called kinase inhibitors. It works by blocking the action of an abnormal FGFR protein that signals cancer cells to multiply. This may help keep cancer cells from growing and may kill them. Giving gemcitabine, cisplatin and durvalumab alternating with pemigatinib may work well for the treatment of unresectable, locally advanced or metastatic biliary tract cancer with FGFR2 alterations.