Oral antibiotic use and early-onset colorectal cancer: findings from a case-control study using a national clinical database

Background: Antibiotic-induced gut dysbiosis has been associated with colorectal cancer (CRC) in older adults. This study will investigate whether an association exists between antibiotic usage and early-onset colorectal cancer (CRC), and also evaluate this in later-onset CRC for comparison. Methods: A case-control study was conducted using primary care data from 1999–2011. Analysis were conducted separately in early-onset CRC cases (diagnosed < 50 years) and later-onset cases (diagnosed ≥ 50 years). Conditional logistic regression was used to calculate odds ratios and 95% confidence intervals (CI) for the associations between antibiotic exposure and CRC by tumour location, adjusting for comorbidities. Results: Seven thousands nine hundred and three CRC cases (445 aged <50 years) and 30,418 controls were identified. Antibiotic consumption was associated with colon cancer in both age-groups, particularly in the early-onset CRC cohort (<50 years: adjusted Odds Ratio (OR_adj) 1.49 (95% CI 1.07, 2.07), p = 0·018; ≥50 years (OR_adj (95% CI) 1.09 (1.01, 1.18), p = 0·029). Antibiotics were not associated with rectal cancer (<50 years: OR_adj (95% CI) 1.17 (0.75, 1.84), p = 0.493; ≥50 years: OR_adj (95% CI) 1.07 (0.96, 1.19), p = 0.238). Conclusion: Our findings suggest antibiotics may have a role in colon tumour formation across all age-groups.