PTEN and breast cancer: To explore the cause of loss of PTEN expression in breast cancer, we treated breast cancer cell lines with the epigenetic inhibitors Trichostatin A (TSA), which inhibits Class I and II histone deacetylases (HDACs), and 5-aza-2′-deoxycitidine (AZA) which is a cytidine analog that blocks DNA methylation (Fig. 1b, c).