Herceptin (Trustzumab) is a monoclonal antibody that specifically targets the HER-2/neu protein and connects to the extracellular receptor and it has been demonstrated that by its presence, treatment leads to improvement in prognosis and survival in patients suffering from gastric adenocarcinoma with over-expression of HER-2/neu (19-22). The gene discussed is ERBB2; the disease is gastric adenocarcinoma.