Causal effect of breast cancer on endometrial cancer risk: A two-sample Mendelian randomization study

Observational studies have indicated a higher incidence of endometrial cancer in individuals with breast cancer. However, to date, there is a dearth of Mendelian randomization (MR) studies that explore the causal relationship between breast cancer and the risk of endometrial cancer.

We conducted MR to investigate the causal relationship between breast cancer and endometrial cancer risk in European populations.

A total of 112 valid instrumental variables (IVs) were included in the analysis. Our research has revealed a compelling causal association between genetic predisposition for breast cancer and an augmented likelihood of developing endometrial cancer (Inverse variance weighted (IVW) method, odds ratio (OR) = 1.105, 95 % confidence interval (CI): 1.025 to 1.181, p = 0.003; Weighted median method, OR = 1.109, 95 % CI: 1.020 to 1.205, p = 0.015; Weighted mode method, OR = 1.101, 95 % CI: 1.013 to 1.195, p = 0.025).

To our knowledge, this study is the first to report a causal association between breast cancer and endometrial cancer risk. Robust results were obtained through rigorous testing for heterogeneity and pleiotropy. Our findings indicate a causal effect of breast cancer on the risk of endometrial cancer.