HealthDay News — There is a positive association between antibiotic use and proximal colon cancer and an inverse association with rectal cancer in women, according to a study published online August 30 in the Journal of the National Cancer Institute.

Sai San Moon Lu, MBBS, MPH, from Umeå University in Sweden, and colleagues conducted a nationwide, population-based study with matched case-control design with 40,545 colorectal cancer (CRC) cases and 202,720 controls to examine antibiotic use in relation to subsequent CRC risk.

The researchers observed a positive association between more frequent antibiotic use and CRC using the full dataset; the results were attenuated toward null when excluding antibiotics prescribed within 2 years of diagnosis. Excluding the 2-year washout, the positive association was confined to the proximal colon in site-specific analyses (adjusted odds ratio for very high use versus no use, 1.17). An inverse association was seen for rectal cancer, which seemed to be driven by women. There was a positive association observed for quinolones and sulfonamides and/or trimethoprim with proximal colon cancer, while across antibiotics classes, a more general inverse association was seen for rectal cancer.

“There is absolutely no cause for alarm simply because you have taken antibiotics,” a coauthor said in a statement. “The increase in risk is moderate and the [effect] on the absolute risk to the individual is fairly small.”

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One author disclosed financial ties to AstraZeneca; a second author disclosed ties to Quretec Bio AB.

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