Colorectal cancer is cancer that affects the large intestine (also known as the colon) or the rectum. The word "colorectal” is just a shortened way of saying colon and rectal.

Colorectal cancer incidence and mortality rates vary markedly around the world. Globally, colorectal cancer is the third most commonly diagnosed cancer in males and the second in females. Rates are substantially higher in males than in females.

Colon or rectal cancer is uncommon before the age 40 years. 90 per cent of cases occur after the age 50, with men at a higher risk than women; therefore, colon cancer screening is usually recommended starting at age 50 for both sexes and repeated after about 10 years if the first colonoscopy was normal or repeated sooner if there was a confirmed non-cancer mass (polyp). It takes approximately 10 years for a small colon polyp to develop into cancer.

Although the exact cause of colorectal cancer is not completely understood, some lifestyle risk factors have been identified. People who mainly depend on a high fat diet, high in red meat or low fibre, have an increased risk of developing colon polyps. Cigarette smoking and obesity is also associated with increased risk of developing these polyps.

Colon cancer tends to run in families, suggesting that genetic factors are also important in their development. Any history of colon cancer in the family should be discussed with a healthcare provider, particularly if cancer is developed at an early age (before the age of 60), in close relatives, or in multiple family members. As a general rule, screening for colon cancer begins at an earlier age (40) in people with a family history of colon cancer.

The most common symptoms of colorectal cancer can include; stomach pain, change in bowel habits (constipation or diarrhoea), blood in the bowel movements, feeling weak or tired, dizziness and other signs of low iron level (iron deficiency anaemia), black or dark-coloured stools.

Colonoscopy is the best test to evaluate the colon because it allows the doctor to see the entire lining of the colon and any precancerous tumours (colon polyps) seen during the procedure can be safely removed during this procedure. During colonoscopy, a doctor inserts a very thin flexible tube with a light source and small camera attached to it into the anus. The tube is advanced through the entire length of the large intestine (colon) so that he or she can visualise the entire lumen of the large intestines for any structural abnormalities, such as polyps, or features of colon or rectal cancer.

Other investigations such as CT scans can be done to determine the extent of the cancer spread (cancer staging).

Most types of colorectal cancer are treated with one or more of these, depending on the stage of the cancer at diagnosis; surgery to remove the part of the colon or rectum that has cancer, medicine called chemotherapy that kills cancer cells or radiation therapy. 

It is important to know that colon or rectal cancer is preventable if precancerous polyps are detected and removed before they become malignant (cancerous). Over time, small polyps can change their structure and become cancerous.

Some lifestyle changes can reduce one’s chances of suffering from colon cancer though to a small extent, such as; eating a diet that is low in fat but high in fruits, vegetables, and fibre. Losing weight, if one is overweight, and quitting or not smoking at all for non-smokers, and limiting the amount of alcohol one takes, can prevent development of colon cancer.

 Dr. Ian Shyaka

Resident in Surgery, Rwanda Military Hospital,

iangashugi@gmail.com