Squamous Cell Carcinoma of Unknown Primary

This phase Ib trial tests the safety, side effects and best dose of tumor membrane vesicle (TMV) vaccine therapy alone and in combination with pembrolizumab and evaluates how well it works in treating patients with head and neck squamous cell cancer that has come back after a period of improvement (recurrent) or that has spread from where it first started (primary site) to other places in the body (metastatic). Vaccines made from a person's tumor cells, such as TMV vaccines, may help the body build an effective immune response to kill tumor cells. Immunotherapy with monoclonal antibodies, such as pembrolizumab, may help the body's immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread. Giving TMV vaccine therapy alone or with pembrolizumab may be safe, tolerable and/or effective in treating patients with recurrent and/or metastatic head and neck squamous cell cancer.