Blood samples from approximately 210 patients diagnosed with colorectal carcinoma collected prospectively and consecutively at the Department of Surgical Gastroenterology, Aalborg University Hospital during the time period 2003-2006 will be used. The blood samples were collected at the time of diagnosis, before and after treatment (surgery and radio-chemo-therapy) and at regular intervals for a time period of two years after treatment. These blood samples were collected during a previous PhD-study: "Pre- and postoperative Venous Thromboembolism in Patients with Colorectal Cancer - implications of Radiotherapy" (ID-number VN 2003/102). In collaboration with the Section of Molecular Diagnostics, Clinical Biochemistry, Aalborg University Hospital, the methylation profile of the cell-free DNA promoter regions in plasma will be analysed using methylation specific PCR (Polymerase Chain Reaction) based on an accelerated bisulfite treatment method.