Study confirms colorectal cancer screening should start at age 50

September 2, 2008

Colorectal adenomas, the precursor polyps in virtually all colorectal cancers, occur infrequently in younger adults, but the rate sharply increases after age 50. Additionally, African Americans have a higher rate of proximal, or right-sided, polyps, and may have a worse prognosis for survival if the polyps become cancerous. Therefore, the results of this study further emphasize the importance of colonoscopies, which view the entire colon, for the prevention of colorectal cancer beginning at age 50.

The results of this study, which represents the largest investigation, by several-fold, of this kind, were published in Clinical Gastroenterology and Hepatology, the official journal of the American Gastroenterological Association (AGA) Institute.

"While colorectal polyps are rare in adults aged 30 to 50, our study reveals an increase in polyp prevalence with age and a dramatic increase in colorectal adenoma incidence occurring in adults over the age of 50," said Francis M. Giardiello, MD, of The John Hopkins University and lead author of the study. "Understanding the natural occurrence of colorectal polyps, especially in younger adults, is important to the development of colorectal cancer prevention strategies."

Researchers found the prevalence of colorectal polyps in younger adults increased from 1.72 percent to 3.59 percent from age 30 to 50. This rate sharply increased after age 50 with the prevalence of polyps ranging from 10.1 to 12.06 percent in the sixth and ninth decade, respectively. The study results quantified the number of adenomas typically found in people under the age of 50. It is important to note that those with two or more adenomas under 50 years of age represent unusual individuals who might merit closer colonoscopic surveillance for subsequent adenoma development.

In younger adults, adenomas were more prevalent in Caucasians compared to African Americans; however, in older adults, the reverse was true. Regardless of age, adenomas were more prevalent in men than women.

In the general population, left-sided adenomas are most common, but among older adults (age 50+), who have more adenomas, there is a relatively greater prevalence of right-sided adenomas. African Americans in both age groups had predominately right-sided polyps.

The use of sigmoidoscopy as a screening test for colorectal cancer does not allow gastroenterologists to view the right-side of the colon to screen for polyps, only the rectum and the lower end of the colon. If a polyp or abnormality is found, patients may require a regular colonoscopy for further evaluation. Right-sided adenomas cannot be viewed using a sigmoidoscopy.

Colonoscopy, which provides the most comprehensive view of the colon, is the definitive test for colorectal cancer screening. Colonoscopies allow gastroenterologists to view the entire colon and rectum for polyps or cancer and during the same exam remove pre-cancerous polyps. It is the test most gastroenterologists recommend as the single best screening exam for colorectal cancer. It is the only method that combines both screening and prevention (by removal of pre-cancerous polyps).

The study evaluated the large intestine of 3,558 autopsy subjects, aged 20-89, that had colorectal cancer undetected or unsuspected during life. Subjects were categorized by sex, race and age in 10 year groups. Location and number of colorectal adenomas detected was measured by using epidemiologic autopsy in individuals; results were standardized to the general population. The study's researchers evaluated the large intestine of 1,001 individuals undergoing necropsy between the ages of 20 and 49 for the presence of adenomas.

Source: American Gastroenterological Association