Therefore, out of all breast cancer cases, we selected four groups (numbered from I to IV) characterized by significantly different levels of ERα (mRNA and protein level) and HSF1 (mRNA) expression: ER−/HSF1low, ER−/HSF1high, ER+/HSF1low, and ER+/HSF1high (Figure 6B). Here, HSF1 is linked to breast cancer.