Lack of ductal development in the absence of functional estrogen receptor alpha delays mammary tumor formation induced by transgenic expression of ErbB2/neu.

Expression of the mouse mammary tumor virus (MMTV) neu/erbB2 transgene in mice induces mammary tumors. To examine the effect of removing estrogen receptor alpha (ERalpha) signaling on the ability of an MMTV-neu/erbB2 transgene to induce mammary tumors, the neu transgene was expressed in the ERalpha knockout (alphaERKO) mouse, which lacks functional ERalpha. MMTV-neu females that lacked ERalpha still developed mammary tumors; however, tumor onset was significantly delayed.