Inflammatory bowel disease and risk of breast cancer: a meta-analysis of cohort studies.

Inflammatory bowel disease (IBD) has been found to be correlated to increased risk of both gastrointestinal and extraintestinal malignancies. It still remains conflicting whether IBD has influence on risk of breast cancer, requesting further investigations. A systematic literature research before June 2020 was conducted in PubMed and Web of Science databases. Observational studies reporting incident breast cancer after IBD diagnosis and providing measures of association were included in the meta-analysis. The pooled odds ratio (OR) with 95% confidence interval (CI) was calculated to evaluate the associations between IBD and risk of breast cancer. Our analysis included 16 cohort studies and the overall pooled OR in patients with IBD was 0.94 (95% CI, 0.82-1.06). In further subgroup analysis, no significant association with breast cancer risk among patients with Crohn's disease (OR, 0.91; 95% CI, 0.70-1.12) and ulcerative colitis (OR, 0.99; 95% CI, 0.90-1.08). For geographic differences, the summary OR of populations in Asia (OR, 1.01; 95% CI, 0.73-1.30) was only numerically larger than that in European populations (OR, 0.90; 95% CI, 0.75-1.06). Our findings indicated that IBD had no significant influence on breast cancer risk regardless of different IBD types and geographical areas.