New research has observed differential benefits of patients’ antibiotic use on their risks of developing colon or rectal cancer. The results suggest that the state of the microbiome may be an important indicator of patients’ gut cancer risks.
Antibiotics lastingly alter the composition and activity of one’s gut-resident bacteria — termed the ‘gut microbiome’. In 2010, it was estimated that 70 million antibiotics were taken worldwide. Now, researchers have assessed the impacts of antibiotic administration on the risks of gut cancer development specifically and observed antibiotics to increase patients’ risk of developing colon cancer whilst decreasing the risk for rectal cancer.
Researchers assessed prescribing information concerning 28,930 patients diagnosed with bowel or rectal cancer, and 137,077 matched comparators, from the Clinical Practice Research Datalink (CPRD; London, UK) — a compilation of anonymized medical records of approximately 11.3 million individuals from 674 UK general practices during 1989–2012.
All patients included in the study had been monitored for, on average, 8 years.
20,278 of the 28,930 patients — equivalent to 70% — that were subsequently diagnosed with bowel or rectal cancer had been prescribed antibiotics.
Similarly, 68.5% of the 137,077 matched study participants, who did not develop these cancers, received antibiotics.
An association between patients’ colon cancer development and their administration of antibiotics was observed when the antibiotics were taken more than 10 years prior to patients’ cancer diagnosis.
Compared with matched controls, patients with colon cancer were more likely to have been prescribed antibiotics targeting either anaerobes or aerobes — bacteria that do not, and do, require oxygen respectively.
By contrast, compared with matched controls, rectal cancer patients had reduced likeliness of having been prescribed antibiotics targeting anaerobes.
Antibiotic class was also associated with gut cancer site; compared with matched, non-cancer patients, individuals who received antibiotics targeting anaerobes were more likely to develop cancer in the proximal colon only — the initial parts of the bowel.
After accounting for potentially confounding factors — including patients’ weight, smoking status and drinking habits — patients’ cumulative use of antibiotics, most notably of the penicillin class and for more than 16 days, correlated with their increased risk of colon cancer development. This impact was greatest for proximal colon cancer.
By contrast, with regards to rectal cancer development, patients’ antibiotic use — particularly of tetracyclines — for more than 60 days was associated with a 15% reduction in cancer development, compared with individuals who did not receive such antibiotics.
However, due to the observational nature of the study, the authors concluded: “Whether antibiotic exposure is causal or contributory to colon cancer risk, our results highlight the importance of judicious antibiotic use by clinicians.”
Zhang J, Haines C, Watson AJM et al. Oral antibiotic use and risk of colorectal cancer in the United Kingdom, 1989—2012: a matched case—control study. Gut; 0:1—8. doi:10.1136/gutjnl-2019-318593 (Epub ahead of print) (2019);