After trastuzumab, other different anti-HER2 monoclonal antibodies including lapatinib (Tykerb®, GlaxoSmithKline, Brentford, United Kingdom), neratinib (Nerlynx®, Puma Biotechnology, Los Angeles, CA, United States), gefitinib (Iressa®, AstraZeneca, Cambridge, United Kingdom), or afatinib (Giotrif®, Boehringer Ingelheim Pharmaceuticals, Inc., Ingelheim am Rhein, Germany) [8] as monotherapy or in combination with conventional treatments have contributed to increasing the number of therapeutic options for breast cancer patients. The gene discussed is ERBB2; the disease is breast cancer.