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Women have higher rate of early CRC after negative colonoscopy, data suggest, possibly because of greater burden of missed proximal lesions at screening

Wednesday, March 24 2010 | Comments

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What's This? A negative colonoscopy is associated with a reduced short-term risk of colorectal cancer (CRC) in men but not in women, according to findings from a study conducted in Manitoba, Canada. According to the study data, this discrepancy might be the result of a higher incidence of proximal CRC cases in women, which are more likely to be missed by colonoscopists during screening.

Researchers reviewed data for 45,985 individuals (women, n=27,379) aged 40 years or older who were members of Manitoba's provincial physician's billing claims database and who had a negative colonoscopy result. All individuals included in the study had been covered by the provincial health plan for >=5 years and had no history of CRC, inflammatory bowel disease, resective colorectal surgery, or lower gastrointestinal endoscopy before the index endoscopy.

The risk of CRC following a negative colonoscopy was compared with the risk of CRC in the general population of the province. The goals of the analysis were to assess differences between men and women in the reduction in CRC risk associated with a negative colonoscopy, differences in the risk of developing proximal versus distal CRC following a negative colonoscopy, and predictors of developing CRC after a negative colonoscopy.

During the entire follow-up period (229,090 person-years), the incidence of CRC among men with a negative colonoscopy was reduced by approximately 40% relative to men from the general population (standardized incidence ratio [SIR], 0.59; 95% CI, 0.50-0.70); the incidence of CRC among women with a negative colonoscopy was reduced by approximately 30% relative to women from the general population (SIR, 0.71; 95% CI, 0.61-0.83).

However, when the investigators assessed the risk of CRC during the first 3 years after a negative colonoscopy (ie, cases potentially resulting from lesions missed during the index procedure), they noted that a negative colonoscopy was associated with a reduced CRC risk in men only. Among women, those with a negative colonoscopy result were no less likely to develop CRC than were women from the general population.

Additional data from the study suggested that this difference might be explained by the higher incidence of proximal CRC cases among women. The authors explained that a negative colonoscopy was associated with a reduced risk of distal CRC in both men and women throughout follow-up. However, a reduction in the risk of proximal CRC was only apparent after 5 years of follow-up. The lack of risk reduction during the first 5 years, they added, likely reflects missed proximal lesions during the index colonoscopy.

In a multivariate model, independent predictors of CRC occurring within 3 years of a negative colonoscopy were older patient age and performance of the index colonoscopy by a nongastroenterologist. By contrast, independent predictors of CRC occurring after 3 years were older age and male sex.

According to the study researchers, the model results support the presumption that "CRCs diagnosed within the first few years of the negative colonoscopy are more likely to be due to lesions missed on the index procedure and those diagnosed later on are more likely to be new (de novo) CRCs." (Singh H, et al. Am J Gastroenterol 2010;105:663-673.)

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