Testing the Addition of an Anti-Cancer Drug, Abemaciclib, to the Usual Chemotherapy Treatment (5-Fluorouracil) for Metastatic, Refractory Colorectal Cancer

This study is testing whether adding abemaciclib — a drug that blocks cancer cell growth — to standard chemotherapy (5-fluorouracil, or 5-FU) can help patients with metastatic colorectal cancer that has stopped responding to multiple prior treatments. **You may be eligible if...** - You are 18 or older with confirmed microsatellite stable (MSS) metastatic colorectal cancer - Your cancer has already progressed on standard chemotherapy combinations including 5-FU, oxaliplatin, and irinotecan - You have also progressed on or been intolerant to bevacizumab - If your tumor is left-sided and RAS wild-type, you must also have received anti-EGFR antibody therapy - You have measurable disease and are in adequate overall health **You may NOT be eligible if...** - You have not yet tried standard chemotherapy combinations - Your cancer has a microsatellite instability-high (MSI-H) profile - You are under 18 - Your organ function is too poor Talk to your doctor to see if this trial is right for you.