PTEN and breast cancer: Preclinical studies have shown that reduced PTEN expression increases cancer cell survival and proliferation, and has been associated with resistance to EGFR inhibitors in NSCLC and colon cancers, and resistance to trastuzumab in breast cancer (Bianco et al, 2003b; Fujita et al, 2006; Berns et al, 2007; Sierra et al, 2010).