In breast cancer, interruption of estrogen receptor (ER)-alpha function is an effective therapeutic strategy. Despite the clinical benefit of interruption of ER-alpha function, the precise biological action of ER-alpha in breast tumors is not completely understood. Results of a recent study show that ER-alpha promotes growth of breast cancer cells by targeting expression of signaling components of the insulin-like growth factor system. Intriguingly, the authors of this study raise the possibility that unliganded ER-alpha itself may affect gene expression and breast cancer biology, and they suggest a potential mechanism for ER-alpha to stimulate proliferation in breast cancer.