Screening for Colorectal Cancer

Colorectal cancer has achieved the status as the most common cancer in Singapore. The rate for men is about 40 per 100,000 individuals or 29 women per 100,000. Colon cancer comes from polyps that form in the colon. If you can remove the polyps before they become cancer, you can prevent the cancer from forming. Early cancers can be removed by removing cancerous polyps. It is recommended that those over the age of 50 be screened for colon cancer. It improves survival rate if you go through the recommended screening tests.

The average lifetime risk of getting colon cancer is about 5 percent. The risk goes up much higher past the age of 50. If you have a family history of colon cancer, you have a much greater risk of developing both polyps and cancer. Those with pelvic radiation or previous uterine or endometrial cancer have a slightly higher risk of developing colon cancer. Those with a history of familial polyposis syndrome are genetically predisposed to having colon cancer and are at an extremely high risk of getting colon cancer.

The screening tests for colon cancer include a fecal occult blood test, colonoscopy, CT coloscopy or virtual colonoscopy and a double contrast barium enema. More recently fecal immunochemistry tests (FIT) have become available. Fecal occult blood tests or fecal immunochemistry tests are recommended yearly at the time of the physical exam. They check for the presence of blood in the stool. The FIT test is more sensitive than the FOBT test.

If there is a positive FIT or FOBT test, a colonoscopy is indicated. A colonoscopy can both visualize and remove any suspicious lesions. It is the gold standard for colon testing. The complications include perforation of the colon in 0.03-0.17 percent of cases and bleeding, which occurs in 0.03-0.09 percent of cases. It reduces the risk of colon cancer by 76 percent when compared to those who didn’t have a colonoscopy. One of the downsides of colonoscopy is the preparation is extensive and complicated. There is a risk of missing a polyp that is about 6-12 percent. Usually it is the low risk polyps that are missed, such as flat or depressed polyps.

Colonoscopy is recommended about every 10 years, sooner if blood is detected. Those with colorectal polyps should have reevaluation with colonoscopy every 3 years. If colon cancer is found, a repeat colonoscopy should be done in about a year to make sure the cancerous area has resolved. Those with low risk polyps found should have a repeat colonoscopy within five years. Those with hereditary polyposis syndrome should have increased screening intervals of 1-2 years. It should start ten years before the youngest person was diagnosed with colon cancer and continue every 1-2 years after that.