ESR1 and breast cancer: After potentially excluding pleiotropic single nucleotide polymorphisms (SNPs) using the MR Pleiotropy RESidual Sum and Outlier method, the odds ratio (OR) for per extra daily cup of tea intake for overall, estrogen receptor (ER)-positive, and ER-negative breast cancer risk was 1.029 [95% confidence interval (CI) = 0.983–1.077, P = 0.2086], 1.050 (95% CI = 0.994–1.109, P = 0.078), and 1.081 (95% CI = 0.990–1.103, P = 0.6513), respectively.