Trastuzumab emtansine was approved by the FDA in February 2013 as a single-agent treatment for HER2-positive, metastatic breast cancer in patients who previously received trastuzumab and a taxane, either separately or in combination [103]; in May 2019, this was extended to include HER2-positive early breast cancer in patients with residual invasive disease after neoadjuvant taxane-based chemotherapy and trastuzumab-based treatment [104]. This evidence concerns the gene ERBB2 and breast carcinoma.