Despite the great leap forward achieved in clinical practice by the use of trastuzumab, as well as the improved outcomes in patients with HER2-positive breast cancer, there are still few problems limiting the use of trastuzumab, including resistance and cardiotoxicity [67,77], not to mention that the promising results of trastuzumab are limited to those patients with particularly high levels of HER2, leaving a large number of breast cancer cases, along with other types of cancers in which HER2 levels range from low to moderate, untreatable [78]. The gene discussed is ERBB2; the disease is breast carcinoma.