A Biomarker Study in Patients Getting Regorafenib for Metastatic Colorectal Cancer

This is an exploratory biomarker study. Patients with metastatic colorectal cancer will receive regorafenib, which is FDA approved in this setting, on day 1-21 of every consecutive 28 day cycle. Patients will be asked to undergo tumor biopsy at baseline and 2 weeks after starting regorafenib. Peripheral blood samples will be collected at baseline 2 weeks after starting regorafenib, after initiation of cycle 3, and every 4 weeks thereafter.