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Most adults under 50 unlikely need colorectal screening

October 01, 2008

New study shows they have few pre-cancerous polyps

Young adults without a family history of bowel disease are unlikely to develop adenomas, the colorectal polyps most likely to lead to cancer, according to new research directed by scientists at the Johns Hopkins Kimmel Cancer Center. The finding supports current cancer screening guidelines recommending adults in general undergo screening colonoscopies starting at age 50.

The new study, published in the September issue of the journal Clinical Gastroenterology and Hepatology, also showed that white patients more often had adenomas on the left side of the colon, whereas African Americans had lesions more often on the right side. The take-home lesson, Giardiello says, is that screening and diagnostic evaluations of African Americans should include a colonoscopy rather than a sigmoidoscopy, because the latter evaluates only part of the colon.

The Hopkins study assessed the "natural history" and occurrence of colorectal polyps by reviewing records of 3,558 autopsies performed at The Johns Hopkins Hospital between 1985 and 2004 on patients aged 20 to 89. The review, called an "epidemiologic necropsy," categorized patients by sex, race and 10-year age groups, then compared the prevalence and location of adenomas between younger adults (ages 20 to 49) and older adults (ages 50 to 89).

The review identified a low but increasing prevalence ofcolorectal adenomas -- from 1.72 percent to 3.59 percent -- from the third to the fifth decade of life, with the presence of adenomas sharply increasing after age 50. Prevalence ranged from 10 to 12 percent from the sixth to ninth decade of life.

"Our study affirmed that the greatest increase in prevalence was in older adults, abruptly starting in the sixth decade," says Francis M. Giardiello, M.D., professor of medicine, oncology and pathology, who directed the research. The average number of adenomas spotted in most young adults was one. In older adults, the average number of adenomas ranged from 1.6 to 1.9.

Most polyps detected in colorectal screenings qualify as adenomas, but there are also lower-risk lesions called "hyperplastic" which are not thought to lead to cancer, the researchers note.

The researchers found that in young adults, adenomas were slightly more prevalent in men than in women and in whites than in blacks. In older adults, the prevalence of adenomas also was greater in men than in women, but greater in blacks than in whites.

In addition, the study found that in both younger and older adults, the overall prevalence of left-sided adenomas was higher than right-sided adenomas. Compared with younger adults, older adults had an increased prevalence of adenomas on both sides of the colorectum, but a relatively greater prevalence of right-sided adenomas.

Johns Hopkins Medical Institutions