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Unclear if family history of adenoma ups colorectal cancer risk

NEW YORK (Reuters Health) – Modern research still can’t answer the question of whether a family history of adenomatous polyps puts patients at higher risk for colorectal cancer, researchers say.

The message of their review in the May 15th Annals of Internal Medicine, according to coauthor Dr. Thomas F. Imperiale from Indiana University, Indianapolis, is, that “those (few) providers who are following those guidelines” that say treat the same as a first degree relative (FDR) with colorectal cancer should not do this, but instead should individualize based on a review of that relative’s age, colonoscopy, and pathology reports.

“It will take some work on the part of patient and provider, but will lead to more sensible, tailored decision-making,” he told Reuters Health in an email.

Dr. David F. Ransohoff from the University of North Carolina in Chapel Hill added, also by email, “The few guidelines that say ‘treat the same as an FDR with colorectal cancer’ are not high-quality in the sense that they are not based on strong evidence, and such guidelines should continue to be treated with salutary neglect. Part of the problem is that guidelines may vary in what they suggest, and some guidelines are more trustworthy than others.”

Dr. Imperiale and Dr. Ransohoff investigated the evidence from 12 published studies cited by organizations that produce guidelines for colorectal screening to determine the validity of recommendations for screening among individuals having FDRs with adenomas.

According to the two authors, 10 of the 12 studies answered the wrong question (“Do persons who have a first-degree relative with colorectal cancer have a higher risk for adenoma?”) rather than addressing whether persons who have an FDR with an adenoma face a higher risk for colorectal cancer.

Only two of the studies (both with methodological limitations) addressed the relevant question. One of those studies found a 4.36-fold increased risk of colorectal cancer (an absolute risk of 2.31%) in persons who have FDRs with adenomas.

The second study showed a 2.27-fold increased risk of colorectal cancer or large adenoma among individuals who have FDRs with large adenomas (at least 1 cm). The difference in colorectal cancer risk alone, however, did not differ significantly between those with and without such a history.

The researchers say the ideal study to address this question would follow two groups over time (FDRs of persons with adenomas versus FDRs of persons without adenomas), measuring the frequency of colorectal cancer in the two groups. This study is unlikely to be done, they say, because it would require so many participants and would take so many years to complete.

A less ideal, but feasible, alternative would be a cross-sectional study to compare the frequency of colorectal cancer in persons with and without FDRs with adenomas.

What to do in the meantime? Dr. Ransohoff suggests, “If there’s no strong evidence for ‘high risk’ in first-degree relatives of persons with adenoma, then we don’t have to screen those persons any differently just because they have relatives with adenomas (as a few guidelines now suggest) — at least until we get better evidence. In contrast, the evidence about first-degree relatives of persons with colon cancer is stronger and more appropriate to act on.”


Ann Intern Med 2012;156:703-709.