Trastuzumab (Tzb and Herceptin) was the first immunotherapeutic drug for the treatment of breast carcinomas overexpressing the HER2 (erbB-2) oncogene that was successful [69–73]; however, the mechanisms that could explain de novo and acquired resistance to anti-HER2 monoclonal are not well understood. Here, ERBB2 is linked to breast carcinoma.