Polyps are (usually) benign growths from the lining of the colon or rectum and often look like mushrooms on a stalk. They may vary in size from a few millimetres to 3-5 centimetres. They may be a co-incidental finding whilst undergoing a colonoscopy or flexible sigmoidoscopy. Most polyps can be removed safely at colonoscopy or flexible sigmoidoscopy and this has been shown in scientific studies to significantly decrease the risk of developing cancer of the colon or rectum in the future. Cancer affecting the large intestine (colon) or back passage (rectum) are common, being only second to breast cancer in non-smoking woman and prostate cancer in non-smoking men. These cancers are infrequent below the age of 65 but may occasionally occur in younger people, especially if there is a close relative with the disease. Symptoms related to cancer of the colon or rectum may be very vague and depend to some degree on the site of the cancer. For example, a cancer in the rectum may present with blood in the stool or a sensation of incomplete evacuation after defaecation (tenesmus); cancer of the first part of the colon (caecum) may lead to anaemia (a fall in haemoglobin) from invisible (occult) bleeding.