HSF1 and cancer: While higher levels of HSF1 expression do positively correlate with HSF1 gene targets in human breast tumor samples (Figure 3), and HSF1 overexpression in cultured cancer cells can lead to increased HSP levels [61,66], HSF1 activation appears to be primarily regulated at the protein level as may be expected when an immediate transcriptional response is required, such as when the HSR is deployed [67].