Inflammatory bowel disease and breast cancer: epidemiological evidence, shared biology, and clinical management.

OBJECTIVE AND

DESIGN

This narrative review examines epidemiological, genetic, mechanistic, microbial, and therapeutic evidence concerning inflammatory bowel disease (IBD) and breast cancer.

METHODS

Relevant literature was identified through targeted PubMed searches completed through May 2026 and reference-list screening. Evidence was selected for its relevance to epidemiology, candidate mechanisms, microbiome-related pathways, and treatment interactions.

RESULTS

Pooled cohort evidence does not show a significant overall increase in breast cancer risk among patients with IBD. Several inflammatory, stromal, microbial, and endocrine pathways are relevant to both diseases, although most evidence comes from separate study populations and experimental models. Studies of patients with prior malignancy have not shown a clear increase in new or recurrent cancer during commonly used IBD therapies, but few analyses have focused specifically on breast cancer. Microbiome-directed treatments have been studied in IBD and, more recently, in oncology; their value for patients with both diseases is unknown.

CONCLUSIONS

Current evidence does not support classifying IBD as a breast cancer risk state. The main clinical concern is the interaction between treatments for the two diseases, which requires individualized assessment and coordinated gastroenterology and oncology care.