(ChemotherapyAdvisor) – Extension of surveillance intervals to 5 years should be considered in patients following detection and removal of at least one high-risk adenoma given the “strongly and significantly reduced risk” of colorectal cancer (CRC), results of a large population-based case-control study reported in the Journal of Clinical Oncology online July 23, 2012.

Noting that “empirical evidence for recommendations of surveillance intervals after detection and removal of adenomas at colonoscopy is still sparse and mostly based on observations of adenoma recurrence,” the study assessed risk of CRC based on time since polypectomy as well as factors relevant for risk stratification, noted Hermann Brenner, MD, MPH, of the German Cancer Research Center in Heidelberg, Germany, and colleagues.

They compared risk of CRC among 2,582 patients with CRC who had at least one adenoma detected at a preceding colonoscopy with 1,798 matched controls who did not have large-bowel endoscopy and assessed time since polypectomy.

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Using the controls as a reference group, adjusted odds ratios of CRC with polypectomy <3 years previously was 0.2; for 3-5 and 6-10 years, it was 0.4, and 0.9, respectively. “Strong, significant risk reduction within 5 years was consistently seen for women and men, younger and older participants, patients with and without high-risk polyps (three or more polyps, at least one polyp ≥1 cm, at least one polyp with villous components), and those with and without polypectomy in the right colon,” the investigators wrote.

Adjusted odds ratios found risk reduction to be particularly strong for left-sided CRC.

“Despite its limitations, our study provides further support for suggestions that surveillance colonoscopy may be postponed to 5 to 10 years after detection and removal of low-risk adenomas and furthermore suggests possible prolongation of surveillance intervals to 5 years, even in the case of high-risk adenomas. As a result of the high proportion of right-sided cancers among interval cancers occurring after polypectomy, sigmoidoscopy would not be a suitable alternative to surveillance colonoscopy. Further and even larger studies are needed to more precisely define surveillance intervals with enhanced risk stratification,” they concluded.