Colorectal cancer screening should start at age 50

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Colorectal adenomas, the precursor polyps in virtually all colorectal cancers, occur infrequently in younger adults, but the rate sharply increases after age 50. The study results, published online in Clinical Gastroenterology and Hepatology, further emphasize the importance of colonoscopies for the prevention of colorectal cancer beginning at age 50.

"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.”

In March 2008, the American Cancer Society adopted virtual colonoscopy as an option for colorectal cancer screening and prevention in average-risk adults age 50 years and older and recommended that this population receive the procedure once every five years.

The results of this study revealed the prevalence of colorectal polyps in younger adults increased from 1.72 to 3.59 percent from age 30 to 50. The 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. The authors said it was 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 and older), 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, according to the researchers.

The study evaluated the large intestine of 3,558 autopsy subjects, aged 20 to 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.