Refractory Microsatellite Stable Colorectal Carcinoma

This phase I trial tests the safety, side effects, and best dose of abemaciclib in combination with 5-fluorouracil and how well it works in treating patients with colorectal cancer that has spread from where it first started (primary site) to other places in the body (metastatic) and that has not responded to treatment (refractory). Abemaciclib, a type of cyclin-dependent kinase inhibitor, blocks certain proteins, which may help keep tumor cells from growing. 5-fluorouracil, a type of antimetabolite, stops cells from making deoxyribonucleic acid (DNA) and may kill tumor cells. Giving abemaciclib in combination with 5-fluorouracil may be safe, tolerable, and/or effective in treating patients with metastatic and refractory colorectal cancer.