Polyposis coli: Also called familial polyposis of the colon. This rare condition is characterised by thousands of polyps throughout the large bowel. These polyps are rarely present before puberty, but are usually present by the age of 25. If left untreated, colorectal cancer will occur in almost all patients by the age of 40. Once these polyps have been detected, patients should have a total colectomy (removal of the colon). Children of those with polyposis coli have a 50 percent risk of the eventual development of the premalignant syndrome and should be screened annually until they are 35.

Non-polyposis syndromes: There seem to be clusters of people who have a predisposition to colorectal cancer with no evidence of multiple polyps. These individuals seem to have risks as high as 50 percent for the development of colorectal cancer. Such families often have a history of multiple primary cancers, frequently, ovarian and endometrial. This population develop the cancers younger, usually in their mid-30s to 40s. Children of these people should also be screened regularly from their early to mid-20s.

Where does cancer of the bowel come from?
Most large bowel cancer, regardless of what has caused it, arises from what are called adenomatous polyps. Adenomatous is a description of the type of cell involved in the cancer. Polyps are visible as outgrowths of the surface (mucosa) of the bowel. However, polyps are commonly found in the large bowels of middle-aged people and less than one percent of them carry on to become cancerous.

However, if an adenomatous polyp is detected by visualising the large bowel, it will be cut off (biopsied) and examined under the microscope to determine whether or not it is pre-malignant. The rest of the bowel will also be carefully examined, since polyps seldom occur singly.

Screening
The idea behind screening for large bowel cancer is that early detection increases the chances of surgical cure. A simple screening test that your GP can carry out is to put a finger in the rectum and then test the stool obtained for blood. In the USA this is recommended routinely for all people over the age of 40. Anyone who has a regular annual medical check-up should insist on this simple, inexpensive test. However, this test, called the faecal occult blood test, is not 100 percent specific. About 35 to 50 percent of patients with documented colorectal cancer have a negative test, mainly because the cancer is too high up for any bleeding to be detected lower down. Or the cancer may not be bleeding at all.

Colonoscopy and sigmoidoscopy are relatively inexpensive, but very invasive investigations and are generally reserved for people who have a positive faecal occult blood test, for those with a family history of the disease and those who have symptoms.

Symptoms
Symptoms vary according to where the tumour is. Lesions higher up the bowel will often present with chronic, insidious blood loss leading to anaemia, so the presenting symptoms will be tiredness or even palpitations and angina if the person is sufficiently anaemic.

Any middle-aged man who is found to be anaemic must be screened for cancer of the bowel.

If the cancer is lower down in the bowel the symptoms are more noticeable, namely a change in bowel habits, which may be either constipation or diarrhoea, bloody or not. There may also be abdominal cramping. Rectal cancers will generally present with pain and bleeding. An advanced cancer will often present with small or large bowel obstruction.

Treatment
As with any cancer, the treatment depends on the stage of the disease. Colorectal cancer is classified according to a system called Duke's classification: the cancer is staged according to whether it is limited to the wall of the bowel, whether it has penetrated the wall of the bowel, whether it involves lymph nodes in the same region of the bowel or whether there is distant spread.

If it is caught early, before it has penetrated the bowel wall, then the five-year survival rate is more than 90 percent. This falls to five percent for those with distant spread.

Treatment is generally surgical, unless the cancer has already spread to other parts of the body, when the only surgery would be to relieve any obstruction present.

Chemotherapy and radiotherapy are also used in conjunction with surgery.

Advances in surgical technique and in chemotherapy mean that, caught early, bowel cancer is potentially curable.

Tumours of the small intestine
These are rare, comprising only 3 to 6 percent of all gastrointestinal cancers. Because they are rare, correct diagnosis is often delayed. Their symptoms are often vague and non-specific. Small bowel cancer should be suspected with unexplained bouts of cramp, abdominal pain, or intermittent obstruction, particularly when inflammatory bowel disease is not present and the patient has had no prior abdominal surgery.

There are many benign small bowel tumours, which are generally still surgically removed because they cause unpleasant symptoms.

Malignant tumours of the small bowel are adenocarcinomas, lymphomas, carcinoid tumours and leiomyosarcomas.

Cancer of the anus
Cancers of the anus account for one to two percent of the malignant tumours of the large bowel.

These occur most commonly in people with a history of chronic anal irritation, such as sexually transmitted anal warts, perianal fissures and/or fistulas, chronic haemorrhoids and a condition called leukoplakia, which presents as patches of white skin and mucosa. This latter is often a sign of cancer in other parts of the body as well.

Homosexual men seem to have an increased risk of anal cancer if they practice anal sex, presumably due to trauma to the anal canal. In heterosexual people anal cancers are more common after the age of 45, and occur more frequently in women than in men.

Symptoms are of pain, bleeding, a sensation of a mass in the anal area and anal itching.

Until recently the only treatment was a radical resection of the tumour, leaving the patient with a colostomy. However, recent advances have seen the development of a combination of radiotherapy and chemotherapy which has resulted in the disappearance of tumours less than five centimetres in diameter in 80 percent of patients. There is a less than ten percent recurrence rate in these people. This means that more than 80 percent of people can be cured of rectal cancer without disfiguring surgery.