Currently, there are no biomarkers validated prospectively in randomized studies for resected colon cancer to determine need for adjuvant chemotherapy. However, circulating tumor DNA (ctDNA) shed into the bloodstream represents a highly specific and sensitive approach (especially with serial monitoring) for identifying microscopic or residual tumor cells in colon cancer patients and may outperform traditional clinical and pathological features in prognosticating risk for recurrence. Colon cancer patients who do not have detectable ctDNA (ctDNA-) are at a much lower risk of recurrence and may not need adjuvant chemotherapy. Furthermore, for colon cancer pts with detectable ctDNA (ctDNA+) who are at a very high risk of recurrence, the optimal adjuvant chemotherapy regimen has not been established. We hypothesize that for pts whose colon cancer has been resected, ctDNA status may be used to risk stratify for making decisions about adjuvant chemotherapy.