Although we have shown that the induction of EMT is associated with acquired resistance to AZD8931, induction of EMT in HER2-driven mouse mammary tumours via expression of an activating PI3K mutation was associated with de novo resistance to HER2-targeted therapies (Hanker et al., 2013), whereas in vitro studies showed that expression of transcription factors that drive EMT was causally related to de novo trastuzumab resistance (Oliveras-Ferraros et al., 2012). The gene discussed is ERBB2; the disease is breast cancer.