TF and breast cancer: Moreover, when using the MR-Egger method in the liberal analysis, we did not identify aggregated directional pleiotropy between the levels of the four iron markers and breast cancer risk (ER-positive breast cancer: intercept −0.005, 0.003, 0.008 and 0.012; ER-negative breast cancer: intercept 0.010, 0.005, −0.001 and 0.017; overall breast cancer: intercept 0.0005 [transferrin] and −0.0004 [ferritin]; all P > 0.05) (Supplementary Figs. 1, 2 and 3).