Therefore, there is potential for f-Hb, along with age, sex and other risk factors to be used to provide a personalised risk of harbouring CRC, and thus empower people to make a truly informed decision about having a colonoscopy, by weighing the risks and disadvantages of the procedure (e.g. bleeding, bowel wall perforation, emotional distress) against their personalised risk of missing a cancer. This evidence concerns the gene GSTM1 and cancer.