<qa>  What is the effect of pembrolizumab and palliative radiation therapy?This phase II trial studies how well pembrolizumab and palliative radiation therapy works in treating patients with esophagus, stomach, or gastroesophageal junction cancer that has spread to other parts of the body. Monoclonal antibodies, such as pembrolizumab, may interfere with the ability of tumor cells to grow and spread. Palliative radiation therapy, such as external beam radiation therapy, uses high energy beams to treat symptoms that are caused by tumors. Giving pembrolizumab together with palliative radiation therapy may work better in treating patients with esophagus, stomach, or gastroesophageal junction cancer that has spread to other parts of the body. 