Ferritin and Serum Iron in a Causal Relationship with Estrogen Receptor-Negative Breast Cancer: a Two-Sample Mendelian Randomization Study.

Background: The aim of this study was to explore the causal relationship between different serum iron statuses (ferritin, transferrin, transferrin saturation, and serum iron) and the occurrence of estrogen receptor (ER)-positive or ER-negative breast cancer.

Methods: The summary data on serum iron status exposure were gathered from the IEU OpenGWAS Project, the UK Biobank, and other databases. Concurrently, the summary data for ER+ and ER- breast cancer are sourced from the Breast Cancer Association Consortium (BCAC). By examining the causal link between iron status and breast cancer, we deployed five distinct Mendelian randomization (MR) algorithms, namely MR-Egger, inverse variance weighted (IVW), weighted median, simple mode, and MR-PRESSO. To assess heterogeneity and horizontal pleiotropy, Cochran's Q and MR-Egger algorithms were applied, respectively.

Results: Elevated ferritin levels are associated with an increased risk of ER-negative breast cancer (OR(IVW) = 1.042, 95% CI (1.005, 1.081), p = 0.025; OR (weighted median) = 1.050, 95% CI (1.001, 1.102), p = 0.046; and OR (MR-PRESSO) = 1.042, 95% CI (1.005, 1.081), p = 0.039). Conversely, an increase in the serum iron level is linked to a reduced risk of ER-negative breast cancer (OR (IVW) = 0.791, 95% CI (0.649, 0.962), p = 0.019; and OR (MR-PRESSO) = 0.791, 95% CI (0.649, 0.962), p = 0.028). However, there is no evidence of a causal relationship between transferrin, transferrin saturation, and ER-negative breast cancer. For ER-positive breast cancer, none of the four different iron statuses demonstrated a causal relationship.

Conclusions: Ferritin is positively correlated with ER-negative breast cancer, while serum iron is negatively associated with ER-negative breast cancer. However, there is no causal relationship between the four iron statuses and ER-positive breast cancer.