Pembrolizumab With Combination Chemotherapy in Treating Participants With Locally Advanced or Metastatic Small Cell/Neuroendocrine Cancers of Urothelium or Prostate

This phase Ib trial studies how well pembrolizumab works with combination chemotherapy in treating participants with small cell/neuroendocrine cancers of the urothelium or prostate that has spread to nearby tissue or lymph nodes or that has spread to other places in the body. Monoclonal antibodies, such as pembrolizumab, may interfere with the ability of tumor cells to grow and spread. Drugs used in chemotherapy, such as etoposide, docetaxel, cisplatin, and carboplatin, work in different ways to stop the growth of tumor cells, either by killing the cells, by stopping them from dividing, or by stopping them from spreading. Giving pembrolizumab with platinum-based chemotherapy may work better in treating participants with small cell/neuroendocrine cancers of the urothelium or prostate.