We have previously shown that the rexinoid LG268 reduces tumor burden and induces regression of established tumors in the MMTV-Neu model, by decreasing cell proliferation and inducing apoptosis.22,23 Moreover, bexarotene prevents the development of tumors in mammary glands.24 Despite the promising efficacy in this model, the mechanism of action for the RXR agonists LG268 and bexarotene remain unknown, mostly because these small molecules fail to induce tumor cell death in vitro. This evidence concerns the gene ERBB2 and neoplasm.