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November 22/29, 2006

Colorectal Cancer Risk Following a Negative Colonoscopy—Reply

Author Affiliations

Letters Section Editor: Robert M. Golub, MD, Senior Editor.

JAMA. 2006;296(20):2436-2438. doi:10.1001/jama.296.20.2437-b

In Reply: We agree with Drs Weiss and Doria-Rose that some CRC cases diagnosed in the first few years after a negative colonoscopy are likely due to malignant transformation of adenomas missed at the index colonoscopy. As we discussed, a stepwise decline in SIRs may be expected with follow-up of a population-based negative-colonoscopy cohort due to the lessening of the missed lesion effect over time.

We also agree that confounding variables could have biased our findings, although confounding by unmeasured variables is a limitation of any nonrandomized clinical study. We accept that CRC incidence in our cohort will be less than expected in the general population due to our exclusion of high-risk patients. However, the magnitude of this effect is likely to be negligible because most CRC still occurs in persons without identifiable risk factors. Moreover, although participants undergoing colonoscopy for symptom evaluation may have a higher prevalence of CRC or advanced adenomas than asymptomatic participants receiving colonoscopy for screening purposes, this should not affect the rate of subsequent development of CRC if the index colonoscopy is normal.