ERRα has been reported to modulate breast cancer cell metabolism, growth, and proliferation through regulation of multiple oncoproteins.26,32 ERRα is especially critical for the growth of ER-negative33 or triple (ER, progesterone receptor, and HER2/neu)-negative breast cancer cells.34,35 The transcriptional activity of ERRα in breast cancer is known to be regulated by receptor tyrosine kinases, such as ERBB2, commonly referred to as HER2,36 and also by epidermal growth factor receptor (EGFR). This evidence concerns the gene PGR and breast carcinoma.