Pathologic Stage IIIB Gastroesophageal Junction Adenocarcinoma

This phase I trial investigates the side effects and best dose of talazoparib when given together with trifluridine/tipiracil for the treatment of patients with colorectal or gastroesophageal cancer that has spread to nearby tissue or lymph nodes (locally advanced) or other places in the body (metastatic). Drugs used in the chemotherapy, such as trifluridine/tipiracil, 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. Talazoparib may stop the growth of tumor cells by blocking some of the enzymes needed for cell growth. Giving talazoparib with trifluridine/ tipiracil may inhibit certain enzymes in the cells that are responsible for tumor cell growth.