Facts About Colon Cancer

Colorectal cancer is very common. It is the 4th most diagnosed cancer and the 2nd leading cause of cancer death in Canada. It is estimated that nearly 24,000 Canadians are diagnosed with colon cancer each year.

Colorectal cancers usually originate in the lining of the inside of the colon or rectum. The large intestine (the large bowel) is made up of the colon and rectum, and it represents the final part of the digestive system. The majority of colorectal cancers develop in a predictable pattern. It originates with a mushroom growth on the inside of the colon or rectum, called a polyp. Most polyps develop into a cancer after an average of 8-10 years. However, it is important to understand that there are different types of polyps and not all polyps become cancer.

Colonoscopy is an effective screening tool to prevent colon cancer. By identifying pre-cancerous polyps, called adenomas, colonoscopy can be used to remove polyps and therefore prevent most colorectal cancers. Many modalities exist to detect polyps, such as fecal occult blood testing and barium enema, but colonoscopy represents the most accurate test. Moreover, if a polyp is suspected on barium enema, a colonoscopy is usually required to remove the polyp, called polypectomy.

A colorectal cancer may not have symptoms until it is large. Symptoms of colorectal cancer are usually vague and non-specific. Some people report abdominal discomfort, a change in bowel habits, rectal bleeding, symptoms of anemia (such as chest pain, dizziness, shortness of breath), and/or weight loss. If a colon cancer is found during a colonoscopy, biopsies of the growth will be taken to confirm the diagnosis. If it is found early, a colorectal cancer can be completely curable.

Risk factors for developing colorectal cancer include advanced age, previous colorectal polyps, personal or family history of colorectal cancer, inflammatory bowel disease (Crohn's disease or ulcerative colitis), alcohol and smoking, diets high in fat and red meat, and rare genetic syndromes. While risk factors help identify people with greater likelihood of developing colorectal cancer, it is important to understand that some people develop colorectal cancer without any risk factors.

Clearly, colorectal cancer is very common in Canada. Cancer Care Ontario and other government organizations are widely promoting screening for colon cancer. In several clinical studies worldwide, colonoscopy has been shown to reduce the occurrence of colon cancer by about 70%. Hopefully, screening colonoscopy will help prevent many colon cancer-related deaths in Canada.