To investigate the potential of HSF1 as a predictive marker for Hsp90 inhibition, we selected seven breast cancer cell lines representing Luminal A (MCF-7, T-47D), Luminal B (BT-474), basal (BT-549, BT-20, MDA-MB-468) and HER2 positive (BT-474, SK-BR-3) subtypes. The gene discussed is ERBB2; the disease is breast carcinoma.