Inflammatory bowel disease and breast cancer: A two-sample bidirectional Mendelian randomization study

Area of Science:

• Genetics
• Oncology
• Gastroenterology

Background:

• Observational studies suggest a correlation between inflammatory bowel disease (IBD) and breast cancer.
• However, evidence for a causal relationship has been lacking.

Purpose of the Study:

• To investigate the bidirectional causality between IBD (including ulcerative colitis [UC] and Crohn disease [CD]) and breast cancer using Mendelian randomization.
• To assess potential biases in the causal estimates through sensitivity analyses.

Main Methods:

• Utilized two-sample Mendelian randomization (MR) analysis.
• Employed comprehensive Genome-Wide Association Study (GWAS) summary data for IBD and breast cancer from the IEU GWAS database.
• Conducted sensitivity analyses to address heterogeneity and pleiotropy.

Main Results:

• Confirmed a bidirectional causal effect between IBD and breast cancer.
• Genetic susceptibility to IBD was associated with increased breast cancer risk (OR=1.053).
• Breast cancer presence was linked to an increased risk of IBD (OR=1.111).
• Crohn disease showed a significant association with breast cancer (OR=1.050), while ulcerative colitis had a suggestive association (OR=1.106).

Conclusions:

• The findings support a bidirectional causal relationship between IBD and breast cancer.
• Specific subtypes of IBD, particularly Crohn disease, show distinct associations with breast cancer risk.
• Understanding these shared risk factors can inform clinical management strategies for both conditions.