Pathologic Stage IIIA Gastroesophageal Junction Adenocarcinoma AJCC v8

This early phase I trial studies the effect of pembrolizumab and lenvatinib in treating patients with gastroesophageal adenocarcinoma that has spread to other places in the body (advanced/metastatic) or cannot be removed by surgery (unresectable). 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. Lenvatinib may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Giving pembrolizumab and lenvatinib may kill more tumor cells.