Microbiome Resource Center
Microbiome Resource Center
August 20, 2019
2 min read

Oral antibiotics tied to colorectal cancer risk

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Certain oral antibiotics are associated with increased risk for colon cancer, while others are linked with reduced rectal cancer risk, according to study results published in Gut.

Cynthia L. Sears, MD, of the Bloomberg-Kimmel Institute for Cancer Immunotherapy at Johns Hopkins University School of Medicine, and colleagues wrote that several previous studies have shown an association between antibiotics and cancer, but they have not explored how that effect is impacted by antibiotic type or tumor location.

“Use of antibiotics, even narrow-spectrum antibiotics, exerts strong, persistent effects on the structure of the gut microbiota and impairs the integrity of the intestinal barrier,” they wrote. “Antibiotics allow for colonization of pathogenic microbes, and thus, may enable colonization with carcinogenic bacteria that induce local inflammation and tumor formation.”

Researchers conducted a matched case-control study using data from the Clinical Practice Research Datalink from 1989 to 2012. They matched 28,980 cases of CRC with 137,077 controls.

Sears and colleagues found that antibiotic use was associated with CRC risk, but the effect varied depending on antibiotic type and location in the colorectum. They identified a dose-dependent increase in colon cancer risk for any antibiotic use. The risk was highest in the proximal colon and with antibiotics with anti-anerobic activity. Penicillin, such as ampicillin and amoxicillin, increased risk for colon cancer (adjusted OR = 1.09; 95% CI, 1.05–1.13)

Researchers wrote that these antibiotics disrupt microbiota in the colon, which mostly comprises anaerobes. That disruption could allow carcinogenic colon microbiota to develop.

Conversely, Sears and colleagues identified an inverse association between antibiotic use and rectal cancers, especially in cases with more than 60 days of antibiotic exposure (aOR = 0.85; 95% CI, 0.79–0.93) compared with no antibiotic exposure. They also found that tetracyclines reduced the risk for rectal cancer (aOR = 0.9; 95% CI, 0.84–0.97).

“More clinical and translational studies are warranted to test the interplay of antibiotics of different activities and class on the colonic anaerobic and aerobic microbiota and mechanisms of carcinogenesis,” Sears and colleagues wrote. “Nonetheless, whether antibiotic exposure is causal or contributory to colon cancer risk, our results highlight the importance of judicious antibiotic use by clinicians.” by Alex Young

Disclosures: Sears reports receiving a grant from Bristol Myers Squibb for research outside the submitted work. Please see the full study for all other authors’ relevant financial disclosures.