a | Normal epithelial cells express low levels of transferrin (TF) receptor 1 (TFR1) and hepcidin and high levels of ferroportin, which collectively lead to a small pool of labile iron. In breast cells, lipocalin 2 (LCN2), in a complex with a siderophore (SD), may further reduce levels of intracellular iron by capturing and effluxing SD-bound iron from these cells, although this is currently hypothetical. b | Cancer cells show increased expression of TFR1 and hepcidin and low levels of ferroportin, which lead to an increased labile iron pool. In breast cancer cells, LCN2, in a complex with SD-bound iron, may serve as a further source of iron. LCN2R, LCN2 receptor.