This study will evaluate circulating tumor DNA (ctDNA) as a prognostic marker and as a monitor of a short-term disease recurrence in surgical resective stage II and stage III colorectal cancer (CRC). The investigators will recruit newly diagnosed CRC patients, systematically collect their blood samples at the following time point: before surgery, one week after surgery, every three months for the first year and every six months for the second year, which are coincidence with the recommended clinical follow-up. Patients' outcome and survival will be tracked. These study will permit assessment of ctDNA as a predictive and surveillant method for a short-term (two years) tumor recurrence in comparison with other parameters.
