There will be recruited approximately 100 control subjects with a positive occult faecal blood but with a normal colonoscopy for blood sampling (28 ml). 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.