Colon, cancer of

A malignant tumour of the colon. First symptoms of the disease include an inexplicable change in bowel movements (either constipation or diarrhoea), blood mixed in with the faeces, and pain in the lower abdomen. Sometimes, there are no symptoms until the tumour has grown big enough to cause an obstruction in the intestine (see intestine, obstruction of) or perforate it (see perforation). A genetic basis has been found for some types of colon cancer. However, in most cases, the precise cause is unknown. Contributory factors include diet: eating a lot of meat and fatty foods and not enough fibre may increase the risk. The disease often occurs in association with other diseases of the colon, such as ulcerative colitis and familial polyposis. The chances of cure depend critically on early diagnosis. Screening for this cancer includes an occult blood test; if the test is positive, sigmoidoscopy and colonoscopy may be carried out. In most cases of colon cancer, a partial colectomy is performed.