The bowel connects the stomach to the anus. It is divided into two parts: the small bowel (also known as the small intestine) and the large bowel (or the large intestine). The small bowel is 3-5 metres in length, and is where most nutrients are absorbed. The large bowel is about 1 metre in length and is made up of the colon and the rectum. The colon finishes absorbing water and electrolytes. The bowel contents are then stored in the rectum until being passed out as faeces.
Nearly all bowel cancers arise in the large bowel, and small bowel cancer is rare. Most bowel cancers develop from small benign growths, called polyps, on the inside lining of the bowel. Not all polyps become cancerous, and the risk of developing cancer in a polyp depends on the type of polyp and its size. A colonoscopy, a procedure in which a flexible tube with a camera is passed through the anus and around the bowel, can detect and remove polyps to reduce the risk of developing bowel cancer.
About 5% of bowel cancers occur as a result of changes in genes that are passed on from one generation to the next (familial bowel cancer). Familial bowel cancer can be diagnosed by special tests to detect these gene changes, and is more common in young patients and those with a strong family history of cancer. Special counselling is available for people with a diagnosis of familial bowel cancer.
Bowel cancer is usually diagnosed by colonoscopy. Biopsies can be taken and polyps can also be removed during colonoscopies. Radiology tests can be used to diagnose bowel cancer, including barium enema and a special type of CT scan called CT colonography.
Surgery to remove the affected part of the bowel is the main treatment for bowel cancer. Additional treatment with chemotherapy is sometimes required, depending on the stage of the cancer. Radiotherapy is sometimes used in addition to surgery and chemotherapy to treat rectal cancer.
The prognosis of bowel cancer depends on the stage. The stage is determined by scans and by examination of the bowel removed at surgery. Patients with stage 1 and 2 bowel cancer have a good chance of being cured with surgery alone. At least half of stage 3 patients can be cured with a combination of surgery and chemotherapy. The prognosis for stage 4 bowel cancer depends on the circumstances. In the best circumstances cure may still be possible.
Stage 1 cancer: The cancer is confined to the lining of the bowel and there is no sign of spreading elsewhere. These cancers are treated with surgery alone and there is a high chance of cure.
Stage 2 cancer: The cancer has penetrated into the deeper layers of the bowel wall, but has not spread to the lymph glands or elsewhere. Stage 2 cancer is usually treated by surgery alone, but chemotherapy may be advised in particular circumstances to reduce the risk of the cancer coming back. These circumstances include bowel blockage or bowel perforation, or particular features of the tumour that the pathologist looks for under the microscope.
Stage 3 cancer: Cancer cells have been detected in the lymph glands that were removed with the bowel at the time of surgery. Stage 3 bowel cancer has a higher chance of coming back, and chemotherapy can reduce the risk of the cancer returning. It is therefore treated with surgery followed by chemotherapy. The treatment of rectal cancer differs in some ways from the treatment of colon cancer. Radiotherapy is often used prior to surgery in rectal cancer to reduce the risk of the cancer coming back in the pelvis. The radiotherapy is usually given, in combination with chemotherapy, prior to surgery. Because the rectum is the very lowest part of the bowel, some patients with rectal cancer will also need a stoma (bag). This is usually temporary, but sometimes it is permanent.
Stage 4 cancer: The cancer has spread to other organs or tissues. It can spread inside the abdomen or to other parts of the body. This type of spread is called metastasis or secondary spread. The liver is the most common organ affected. Stage 4 disease can sometimes be cured by surgery, usually in combination with chemotherapy. However, it is often not possible to cure stage 4 colon cancer. If this is the case, treatment may be able to control the cancer for some time. Treatment may also reduce symptoms and help provide a better quality of life.
Bowel cancer also called colorectal cancer, is the most common type of gut cancer. New Zealand has one of the highest rates of bowel cancer in the world with over 3,395 new cases diagnosed each year. Of these, small intestinal cancer is not as common, with just over 136 cases diagnosed each year. Anal cancer is also rare, with around 70-80 new diagnoses a year.