COLORECTAL CANCER : A CLEAR AND PRESENT DANGER

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Singapore and Malaysia have one of the highest numbers of colorectal cancers in Asia. Not unlike that observed in Caucasian populations, more than 75 percent of colon cancers affect the left sided colon (splenic flexure, descending, sigmoid and rectum) with the rest occurring in the caecum, ascending, hepatic flexure and transverse colon.

RISK FACTORS

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Lifestyle

While smoking, lack of exercise and alcohol intake show tenuous links with colon cancer, increase dietary intake of fat and animal protein have demonstrated more consistent associations with Increase risk of colorectal cancer. Fibre and calcium ingestion seem to lower the risks. The evidence is by no means conclusive although various hypotheses have emerged to explain the possible mechanisms.

Colonic Polyps

Between 70 and 90 percent of colorectal cancers arise from polyps. Larger (10 mm or more) polyps have a greater potential for malignancy while small polyps (5 mm or less in diameter) have a negligible malignant potential.

The average time from onset of a polyp to onset of cancer, termed the “dwell time,” is 10 to 15 years. This dwell time appears to vary with the location of the cancer - longer in the distal colon than in the proximal colon.

Genetic Factors

A family history of colorectal cancer or polyps increases the risk of colorectal cancer. In general, closer familial relationships to affected relatives, younger age of affected relatives and larger numbers of affected relatives increase this risk. A family history of having a first degree relative (parent or sibling) develop colorectal cancer before the age of 60 or having at least two first degree relatives with these conditions imparts an increased risk for colorectal cancer.

Familial adenomatous polyposis is a genetic condition in which hundreds of polyps develop in the colon and other parts of the gastrointestinal tract, beginning early in life. Persons with familial adenomatous polyposis have an almost 100 percent chance of developing colon cancer by the age of 40.

In hereditary nonpolyposis colon cancer, a strongly inherited tendency for colon cancer is associated with far fewer polyps than occur in familial adenomatous polyposis. Up to 6 percent of colon cancers occur in association with this disorder, which is also called Lynch syndrome. Invariably, about 75 percent of patients with the Lynch syndrome will have colon cancer by the age of 65 years.

Find a Colorectal Surgeon

Expert Author:

Dr Chen Chung Ming, Nobel Surgery Centre