In the case of HER2-positive tumors, the first-line treatment is humanized anti-HER2 monoclonal antibodies (mAbs): trastuzumab (Herceptin), introduced in 1998, and pertuzumab (Perjeta), introduced in 2012 as one of the first immunotherapies approved for the treatment of breast cancer [62]. The gene discussed is ERBB2; the disease is breast cancer.