The role of the intestinal microbiome in regulating local immunity is clear, and studies have shown that the bacterial makeup of the large and small intestine can influence the development of colorectal cancer (CRC). However, little is known about the relationship between antibiotic use and cancer risk. In a study recently published in Gut, the authors found that even a single course of antibiotics can significantly increase the risk of CRC. The matched case-control study of patients in the United Kingdom evaluated 28,980 patients with CRC and 137,077 healthy controls to determine the link between antibiotic use and rates of CRC.
At a median follow-up of 8.1 years, the study found a significant link between oral antibiotic use and increased risk of colon cancer (71.3% vs 69.1%; P < .001). Risk increased in a dose-dependent fashion, with higher antibiotic doses associated with greater incidence of colon cancer. However, even minimal antibiotic use was associated with increased risk and risk of colon cancer plateaued after 60 cumulative days of antibiotic exposure. Antibiotics targeting antianaerobic activity were associated with highest rates of cancer. Increased risk of colon cancer was seen in patients taking penicillin-class antibiotics, while those taking tetracyclines had decreased rates of rectal cancer. Cancers associated with antibiotic use were significantly more likely to occur in the colon than in the rectum (P < .001) and in the proximal colon compared to the distal colon (P = .019).
Other risk factors associated with increased risk of CRC included high body mass index (BMI), history of smoking, moderate to heavy alcohol use, and diabetes. When adjusted for these risk factors, the association between antibiotic use and colon cancer risk increased.
The investigators concluded that antibiotic use can increase the risk of colon cancer, while patients taking antibiotics had a lower risk of rectal cancer. The authors hypothesize that differences in the gut microbiota throughout the colon and rectum may account for this discrepancy. Further studies evaluating the antibiotic microbiome link as it relates to cancer risk will be needed to further clarify this relationship.
Read more about this study on Medscape Oncology.