Association Between Antibiotic Exposure and Colorectal Cancer

A recent large study revealed an association between antibiotic exposure and colorectal cancer, particularly in the proximal colon (NEJM JW Gastroenterol Oct 2019 and Gut 2019; 68:1971). The results were plausible, given experimental evidence that the gut microbiome might have a role in carcinogenesis. Now, Swedish researchers have used nationwide cancer and drug-prescribing registries in a case-control comparison between 40,000 patients with newly diagnosed colorectal cancer (67% in the colon, 33% in the rectum) and 200,000 matched controls. The median time for exposure to antibiotics (prior to colorectal cancer diagnosis) was 6 years, but this interval was as long as 9 years in some cases.

A significant dose-response association between colon cancer and antibiotic use was noted in analyses that were adjusted for potential confounders and excluded antibiotic exposure within 2 years of cancer diagnosis (to minimize reverse causation). Risk was highest in the proximal colon (adjusted odds ratio, 1.17 for very high antibiotic use). In contrast, very high antibiotic use was associated inversely with rectal cancer (aOR, 0.91).