To examine if endogenous ERα interacts with endogenous Hsp70-1/Hsc70 and determine the subcellular site where the ERα-Hsp70-1/Hsc70 interactions occur in ERα-positive breast cancer cells, we performed IPs using cytosolic and nuclear proteins of human breast cancer MCF7 cells as starting materials, respectively. This evidence concerns the gene ESR1 and breast carcinoma.