Colon Cancer
(Colorectal Cancer · Cancer of the Colon)
In this condition factsheet:
The Facts on Colon Cancer
The colon is what we commonly call the last ~2 metres of the intestines, which leads from the small intestine to the rectum. The colon is sometimes referred to as the large intestine. The last part of the large intestine is the rectum.
Colon and rectal cancer, also called colorectal cancer, is the third most common cancer in Canada.
The risk of colorectal cancer increases as a person gets older. Most doctors start screening at age 50. Men appear to be at greater risk for developing colon cancer.
Screening is crucial because colorectal cancer responds best to treatment if caught early. Treatment is most effective for people with localized colorectal cancer. People who may be at higher risk for colorectal cancer should speak with their doctor to decide on the best screening schedule for them.
The stage of a tumour is usually the best way of knowing its curability. Most cancers are staged or graded according to their size and, above all, the degree to which they have spread to other parts of the body. The stage depends heavily on whether lymph nodes are involved. Lymph nodes are bean-shaped concentrations of immune system cells that are found all over the body. They are interconnected by their own network of tubes, called the lymphatic system. Cancer often spreads through the lymphatic system to reach other organs – this jumping from one part of the body to another is called metastasis.
In colon cancer, stage 0 means that the cancer cells are in the inner lining of the colon but haven't reached past the muscle layer. Stages 1 and 2 represent increasing degrees of penetration of the colon's wall. Stage 3 cancer has reached the nearby lymph nodes. Stage 4 has spread to other parts of the body (metastasized). Recurrent cancer has come back after an apparently successful treatment, often reappearing in the liver or lungs instead of the colon.
Causes of Colon Cancer
The causes of cancer are still not understood. Sometimes the genes that control a cell's activity mutate and start giving instructions that lead to runaway growth of tissue. A single cancerous cell divides millions of times, producing a tumour. The tumour builds its own blood vessels to ensure its supply of oxygen. See the general article on cancer for more on the causes and development of cancer.
By observing cancer rates, experts can predict who is most at risk of colon cancer, and it also helps them find ways to predict it in individuals.
The greatest risk factor, and the clearest warning sign, is colorectal polyps. These are benign growths (not in themselves cancerous) in the inside of the colon. However, many benign growths are bad for you, and some are likely to turn into cancer. Polyps belong to this last category.
A polyp usually looks like a ball on a stalk, protruding from the inner wall of the colon. It may cause rectal bleeding, though this is often hidden in the stool. The average polyp has a 5% to 10% chance of becoming cancerous, and larger polyps are more likely to become cancerous. Some people have more than 1 polyp.
You are more at risk for polyps and colon cancer if you:
- are over 50 years of age
- smoke
- drink
- don't get enough exercise
- eat a diet heavy in red meat or processed meat
- have history of ulcerative colitis or Crohn's disease
- have family history of polyps, colon cancer, or cancers of female reproductive organs (ovarian cancer, endometrial cancer, breast cancer)
- are obese
- have diabetes
- have received abdominal radiation (e.g., are an adult survivor of childhood cancer who received abdominal radiation)
Like most cancers, colon cancer appears to be partly genetic and partly environmental, and may be partly random. Some families have genes that cause them to develop thousands of polyps and give them a high probability of colon cancer. Other families lack this gene, but still have a higher incidence of colon cancer than the general population. At the same time, people whose families have never known the disease can be struck by colon cancer.
Symptoms and Complications of Colon Cancer
Polyps and colon cancer may cause slow, steady bleeding in the colon. The blood emerges with the stool but is often invisible. Many other conditions can cause blood in the stool, but if you experience it you should consult a doctor. Often, the blood loss isn't seen, but its effect is felt as iron-deficient anemia. Men and postmenopausal women with symptoms of anemia need a checkup.
Colon cancer can cause vague symptoms like weight loss or change in bowel habits, or it can cause no symptoms at all. More often, colon cancer has no symptoms until the disease is advanced. That's why screening is so vital.
