In addition, oncogenic activation of PIK3CA leads to intrinsic resistance of HER2-positive breast cancer cells to HER2 inhibition (Berns et al., 2007; Hanker et al., 2013), and is more frequently activated in patients that exhibit acquired resistance to HER2 inhibition (Chandarlapaty et al., 2012). The gene discussed is ERBB2; the disease is breast carcinoma.