EGFR and breast cancer: We can conclude that, even though the regulation of mammary tumor growth and survival by ERs and EGFR family members and the biology of β4 integrin in tumors are not completely known, our in vitro and in vivo results provide strong evidence of a functional cooperation among these factors in supporting the survival of mammary tumors and this cooperation in ERβ1-negative tumors may result in a decreased responsiveness to TAM therapy.