TAS-102 With or Without Celecoxib in ctDNA-defined Minimal Residual Disease in Colorectal Cancer After Completion of Adjuvant Chemotherapy

Primary Objectives: The primary objective is to determine the 6-month ctDNA clearance rate in colorectal cancer patients with minimal residual disease following 6 months of TAS-102 therapy. Secondary Objectives: * To determine the 3-month ctDNA clearance rate in colorectal cancer patients with minimal residual disease. * To determine the disease free survival (DFS) amongst colorectal cancer patients with minimal residual disease following 6 months of TAS-102 therapy. * To determine the overall survival (OS) amongst colorectal cancer patients with minimal residual disease following 6 months of TAS-102 therapy. * To determine the safety and tolerability of TAS-102 for the treatment of colorectal cancer patients with minimal residual disease. Exploratory Objectives: * To determine markers of response and resistance in archival tumor tissue including but not limited to immune profiles of tumor-infiltrating lymphocytes, expression of immune markers in tumor cells and microenvironment, and molecular markers (including but not limited to mutations, deletions, and/or amplifications or cancer molecular subtype) * To determine changes in profiles of circulating lymphocytes and ctDNA with treatment * To determine baseline characteristics in archival tumor and/or plasma that may predict clinical benefit