CoLiQ is a clinical study designed to evaluate the clinical usefulness of circulating tumor DNA (ctDNA) markers found in blood, as a liquid biopsy for diagnosis, prognosis and follow-up of colorectal cancer. The main questions it aims to answer are: 1) Can a panel of ctDNA markers identify CRC patients among the other patients summoned for colonoscopy? and 2) Does the type, number and level of ctDNA markers vary with the subtype and clinical course of CRC? Participants will be asked to answer a questionnaire and give a blood sample at inclusion. In addition, patients with CRC will be asked to give an extra test tube at their routine treatment and follow-up blood sampling.