Taking all the above into consideration together with previous data showing that HSP90α is secreted from fibrosarcoma cells and promotes their invasive capacity through association with MMP2 [15], in the present work we sought to investigate the secretion of both the α and the β isoforms of HSP90 in the conditioned medium of MDAMB453 human breast cancer cells and their possible interaction with MMP2 and/or MMP9. The gene discussed is MMP9; the disease is breast carcinoma.