Histone deacetylases (HDACs) are enzymes that epigenetically modify nucleosomes repressing the transcription of certain genes. HDACs can also modify non-histone target proteins altering their function. Understanding the diverse functions of HDACs has lead to an in depth study of the relationship between HDACs and cancer. Since the increased deacetylation of histones leads to increased cell proliferation, angiogenesis and invasion, the use of HDAC inhibitors (HDACi) may be a new therapeutic strategy. HDACi promotes cell cycle arrest, apoptosis and cell differentiation, while preventing angiogenesis. Previous studies have shown a decrease in cell viability, proliferation, and motility with the use of HDACi. Recent investigations are directed towards elucidating the mechanism through which misregulation of HDACs promotes invasion. Currently, we are investigating the role of HDACi on non-histone target Hsp90 and its subsequent effect on the Her2 s ignaling pathway in mammary tumorigenesis.