Patients in the Prospective Dutch ColoRectal Cancer cohort (PLCRC) with non-metastatic colon cancer that gave consent for additional blood withdrawals are enrolled in the observational PLCRC-MEDOCC substudy. In this study, blood is collected before surgery, after surgery and during follow-up. Within PLCRC-MEDOCC, patients with stage II colon cancer that are not considered to have an indication for adjuvant chemotherapy, can be included in the MEDOCC-CrEATE subcohort under the condition that they gave informed consent in PLCRC for biobanking of tissue and for future studies (Trial within Cohorts design). Patients included in MEDOCC-CrEATE will be randomized 1:1 to the (A) ctDNA-based treatment group versus (B) the standard of care group. A total of 1320 patients will be randomized. Patients randomized to the ctDNA-based treatment group will have their post-surgery samples analysed directly after informed consent for MEDOCC-CrEATE. All patients with detectable ctDNA will be offered adjuvant chemotherapy (3 months CAPOX). Patients with undetectable ctDNA will receive routine follow-up at the surgical department. The aim of this Trial within Cohorts study is to investigate how many patients with detectable ctDNA after surgery start with adjuvant chemotherapy.