Causal relationship between other diseases of digestive system and breast cancer: A 2-sample Mendelian randomization study

Abstract

Objective: To assess the causality between other diseases of digestive system and breast cancer.
Method: The 2-sample Mendelian randomisation study was conducted in 2023 at the First Affiliated Hospital of Bengbu
Medical University, Bengbu, China, using data obtained from genome-wide association studies. A 2-sample Mendelian
randomisation was done and inverse variance weighting was the major method to estimate the causality. The
supplementary methods were Mendelian randomisation-Egger, weighted median, simple mode and weighted mode.
Sensitivity analysis, heterogeneity and pleiotropy tests were used for ensuring the reliability of the findings.
Results: A causality was noted between other diseases of the digestive system and breast cancer utilising inverse variance
weighting method (inverse variance-weighted odds ratios (ORIVW)=0.030429786, penalized inverse-variance weighted
(PIVW) =0.024714444). The outcomes of supplementary methods were in line with that of inverse variance weighting
method. In the reverse Mendelian randomisation analysis, there was no clear causal relationship between other diseases
of the digestive system and breast cancer (p>0.05). Multivariate Mendelian randomisation analysis demonstrated that after
adjusting for the influence of oestrogen, other diseases of the digestive system still had a significant direct impact on BC.
Conclusion: A causal relationship was noted between other diseases of the digestive system and breast cancer.
Keywords: Breast cancer, Digestive system, Oestrogen, Mendelian randomisation.