A bidirectional Mendelian randomization analysis of the causal relationship between inflammatory bowel disease and breast cancer based on estrogen receptor status

The incidence of patients diagnosed with either breast cancer (BC) or inflammatory bowel disease (IBD) is increasing each year. IBD has been shown to be strongly associated with the development of a variety of solid tumors, but the relationship with breast cancer is not yet definitive. We explored the causative relationship between IBD and BC using a Mendelian randomization (MR) strategy. MR-Egger regression, weighted median (WM), simple median (SM), maximum likelihood (ML), and inverse variance weighting (IVW) methods were among the analytical techniques used in this work. The examination of heterogeneity was conducted by the use of Cochran's Q test and Rucker's Q test. The sensitivity analysis in this study used the IVW and MR-Egger methodologies. The results of our investigation suggested that IBD had a beneficial impact on estrogen receptor-negative (ER-) breast cancer (odds ratio (OR) = 0.92, P = 0.02). The study did not find a significant association between IBD and the risk of developing overall breast cancer (OR = 0.99, P = 0.60), as well as estrogen receptor-positive (ER+) breast cancer (OR = 1.02, P = 0.60) specifically. In addition, our study findings indicated that there was a detrimental association between ER+ breast cancer and IBD as determined using reverse MR analysis (OR = 1.07, P = 0.04). Furthermore, this analysis failed to observe any significant association between overall breast cancer (OR = 1.07, P = 0.07) or ER- breast cancer (OR = 0.99, P = 0.89) and IBD. Our bidirectional MR study yielded a correlation between IBD and some specific hormone receptor status of BC.