PGR and breast cancer: In MDA-MB-231 cells (triple-negative human breast cancer cells (TNBC) ER-/PR-/HER2-), the inhibition of extracellular Hsp70 (isoform not identified in the original publication) suppresses tumor invasion of surrounding normal tissue through the Hsp90-dependent activation of matrix metalloproteinase-2 (MMP-2) [72].