Regorafenib and XmAb20717 in Treatment of High-risk Patients With Colorectal Cancer With Radiographic Occult Molecular Residual Disease After End of Established Definitive Therapy (RX-CROME)

Primary Objective: 1\. To determine the 6-month circulating tumor (ctDNA) clearance rate following 6 months of therapy with regorafenib and XmAb20717 (RX regimen) in patients with colorectal cancer (CRC) who present with radiographic occult molecular residual disease (MRD) after completing definitive standard-of-care (SOC) therapy. Secondary Objectives: 1. To determine the 3-month ctDNA clearance rate following RX treatment. 2. To determine disease-free survival (DFS) following 6 months of RX treatment. 3. To determine overall survival (OS) following 6 months of RX treatment. 4. To determine the safety and tolerability of RX. Exploratory Objectives: 1. To determine changes in profiles of circulating lymphocytes and ctDNA (including time to ctDNA negative status, duration of ctDNA negative status, overall ctDNA negative rate, lead time from ctDNA detection to radiographic detection) during and following treatment with RX. 2. To determine baseline characteristics in archival tumor and/or plasma that may predict clinical benefit or lack thereof (including but not limited to immune profiles of tumor-infiltrating lymphocytes, expression of immune markers in tumor cells and microenvironment, and tumor molecular profile).