Antibiotic use (pills/capsules) is linked to a heightened risk of bowel (colon) cancer, but a lower risk of rectal cancer, and depends, to some extent, on the type and class of drug prescribed, suggests research published online in the journal Gut.
The findings suggest a pattern of risk that may be linked to differences in gut microbiome (bacteria) activity along the length of the bowel and reiterate the importance of judicious prescribing, say the researchers.
Patients who developed bowel cancer were more likely to have been prescribed antibiotics targeting anaerobes, which don't need oxygen, as well as those targeting aerobes, which do—than patients without cancer.
But patients with rectal cancer were less likely to have been prescribed antibiotics targeting aerobic bacteria.
Cancer site was also associated with antibiotic use. Cancer of the proximal colon—the first and middle parts of the bowel—was associated with the use of antibiotics targeting anaerobes, when compared to people without cancer.
But antibiotic use was not associated with cancer of the distal colon—the last part of the bowel.
After taking account of potentially influential factors, such as overweight, smoking, and moderate to heavy drinking, cumulative use of antibiotics for a relatively short period (16+ days) was associated with a heightened risk of bowel cancer, with the impact strongest for cancers of the proximal colon.
The reverse was true for rectal cancers, where antibiotic use exceeding 60 days was associated with a 15% lower risk compared with no use.
When the analysis was restricted to patients who had been prescribed only one class of antibiotic, as opposed to none, penicillins were consistently associated with a heightened risk of bowel cancer of the proximal colon. Ampicillin/amoxicillin was the penicillin most commonly prescribed to these patients.
By contrast, the lower risk of rectal cancer was associated with prescriptions of tetracyclines.