In accordance with these data, recent studies highlighted that continued use of trastuzumab in HER2+ breast cancer, with loss of PTEN function, induces the epithelial-mesenchymal transition (EMT) and transforms HER2+ to a more aggressive triple negative breast cancer cell type, endowed with increased proliferation and metastatic potential in vivo [178,179]. The gene discussed is PTEN; the disease is breast cancer.