ESR1 and breast cancer: Moreover, Hsp90 was found to interact with a number of proteins important for breast cancer, for example the hypoxia inducible factor HIF-1α, estrogen receptor α, anti-apoptotic kinase Akt, tumor suppressor protein p53, and the ErbB receptor tyrosine kinase (see https://www.picard.ch/downloads/Hsp90facts.pdf for a comprehensive overview and references).