Use of oral antibiotics is linked to an increased colon cancer risk, but reduced risk of cancer in rectum shows a large matched case-control study. The association between cancer and antibiotic use was seen when antibiotics had been used more than 10 years before diagnosis.
The cancer risk is dose-dependent for any antibiotics although the risk increases most with anti-anaerobic antibiotics and especially penicillin. Penicillin significantly increases the risk of cancer in the proximal colon.
Oral antibiotic use and risk of colorectal cancer in the United Kingdom, 1989-2012: a matched case-control study. Doi:10.1136/gutjnl-2019-318593