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Use of antibiotics may lead to an increased risk of colon cancer at all ages, an analysis of a large Scottish primary care database suggested.

Specifically, the study found that use of antibiotics was associated with an increased risk of colon cancer in both patients over age 50 (adjusted OR 1.09, 95% CI 1.01-1.18) and especially under age 50 (adjusted OR 1.49, 95% CI 1.07-2.07), reported Sarah Perrott, of the University of Aberdeen in Scotland, during a presentation at the virtual .

"With cases of colorectal cancer increasing among young, non-obese patients with no risk factors, our study provides further reasons to reduce, where possible, frequent and unnecessary antibiotic prescribing," she said.

Perrott pointed out that the incidence of early-onset colorectal cancer has been increasing globally, while at the same time there has been an increase in antibiotic consumption. "Significantly altering gut microbiome structure and diversity with antibiotic therapy has been previously shown to influence colorectal cancer genesis in older adults," she noted.

For this nested case-control study, the researchers identified 7,903 colorectal cancer cases (5,281 colon cancers and 2,622 rectal cancers) diagnosed from 1999 to 2011 and matched them with 30,418 controls. Of the patients with colorectal cancer, 445 were under the age of 50, and 45% were prescribed antibiotics during the exposure period.

Perrott and colleagues also found that antibiotic use was associated with an increased risk of proximal colon cancer in patients under 50 (adjusted OR 3.78, 95% CI 1.60-8.92), but not among those in the older age group (adjusted OR 0.89, 95% CI 0.72-1.11).

"No association was observed with rectal cancer," Perrott pointed out, "which we find interesting, in that rectal cancer is a common cancer site in early-onset colorectal cancer compared to later onset."

Most classes of antibiotics were not significantly associated with colon, rectal, or distal colon cancers, the authors reported. However, quinolones (adjusted OR 7.47, 95% CI 1.40-39.94) and sulfonamides/trimethoprim (adjusted OR 4.66, 95% CI 1.66-13.09) were associated with proximal colon cancer in the early-onset group.

"More epidemiological and translational studies are required to evaluate the true role of antibiotics in the development of colorectal cancer and also to evaluate the long-term effects of antibiotics on gut health," Perrott said.

Antibiotic use may be contributing to the increase in early-onset colorectal cancer, said study discussant Thomas Seufferlein, MD, PhD, of Ulm University in Germany.

"However, there are lots of lifetime exposures with potential effects on colorectal cancer tumorigenesis," he noted. "More studies are needed concerning the change in microbiota upon exposure to different antibiotics, and at various ages."

"I agree with the authors that careful use of antibiotics is sensible and paramount," Seufferlein added. "But we are looking for more data on this very interesting topic."

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