In concordance with the previous results, basal activities of HSF1 defined by Hsp70/CHIP ratio also negatively correlate with the IC20 values of breast cancer cell lines to Hsp90 inhibitors, with correlation coefficients of -0.7111 for NVP-AUY922 (p = 0.0171), -0.6597 for BIIB021 (p = 0.0265) and -0.591 for AT13387 (p = 0.0435). This evidence concerns the gene HSF1 and breast carcinoma.