HSF1 and cancer: HSP90/HSF1 feedback system—HSP90 binds to and keeps the inactivated status of HSF1, whereas HSP90 inhibitors trigger the release of HSF1 from the HSP90/HSF1 complex and the subsequent trans-activation of HSP genes, e.g., a compensatory increase in HSP70 expression and other numerous genes, which induce a stress response and resistance of cancer cells.