Viewer Question: If colon cancer is easily detected and it usually starts out as a polyp before turning into cancer then why are there so many cases of it? If a person gets a sigmoid or colonoscopy or barium enema on a regular basis then would that now prevent most colon cancers?

Doctor's Answer: The viewer is correct, colorectal cancer is both preventable and curable. Colorectal cancer is preventable by removing pre-cancerous colon polyps. It is curable if early cancer is surgically removed before cancer spreads to other parts of the body. The National Polyp Study showed that in their surveillance program, the individuals who had their polyps removed experienced a 90% reduction in the incidence of colorectal cancer. The few patients in the study that did develop colon cancers were discovered at early curable stages. Colon Cancer screening is clearly important in cancer prevention.

The issue is whether current colon cancer screening recommendations are adequate. Should regular colonoscopies be performed for screening?

For healthy middle-aged individuals with average risk of colon cancer, current screening recommendations include yearly stool testing for occult blood (trace amount of blood not visible to human eye), and flexible sigmoidoscopies every 3-5 years. For individuals with higher risks of developing colon cancer (individuals with family history of colon polyps and cancer, individuals with prior history of colon polyps, etc.), periodic colonoscopies (examination of the entire colon) are currently recommended.

Flexible sigmoidoscopy is used by the doctor to examine the rectum and the part of the left colon adjacent to the rectum. It is a shorter, less complete version of colonoscopy. Together, fecal occult blood and flexible sigmoidoscopies will not be able to detect all the colon polyps and will detect no more than 25% of colon cancers.

Some doctors have proposed a screening strategy of a single colonoscopy at age 50 in all people. Individuals found to have polyps (therefore at higher risk for colon cancer) will then undergo periodic colonoscopies to detect and remove polyps or early cancer. The value of a colonoscopy for all people at age 50 is presently being debated.

The viewer is absolutely correct. We are still seeing too many advanced colon cancers while technologies and strategies are available for their prevention and early detection. Through education (of both patients and doctors) and wider application of screening recommendations, we should witness a decrease in advanced colon cancers.

Thank you for your question.