Prognosis factors such as mutated or amplified oncogenes are used in the treatment of breast cancer. We have recently shown that the members of the PEA3 group (ER81, ERM and PEA3) from the transcription factor family of the ets genes are overexpressed in breast cancer tumors arising from MMTV-neu transgenic animals. Moreover, we have shown that ER81, and in a lesser extent ERM and PEA3, are not expressed in the estrogen and/or progesterone receptor-positive mammary cancer cell lines, whereas they are expressed in the receptor negative ones. Our research interest in now focused on the role(s) of these oncogenes in the development and the regulation of breast tumors.