ERBB2 and breast carcinoma: Notably, of over 700 identified Hsp90 clients (www.picard.ch/downloads/Hsp90interactors.pdf), many are oncoproteins, including oncogenic drivers of breast cancer (e.g., estrogen and progesterone receptors, BRCA1/2), components of the HER2 signaling pathway (HER2, its co-receptor EGFR, downstream effectors Raf1, Erk, Akt, mTOR), and common mediators of therapeutic resistance in breast and other cancers (e.g., mutant HER2 and EGFR, HER3, IGF-1R)12–15,19–23.