The U.S. Food and Drug Administration (FDA) approved patuximab, a novel anti-HER2-positive therapy, on June 8, 2012 for the treatment of patients with advanced metastatic breast cancer who are anti-human epidermal growth factor receptor 2 (HER2)-positive. Patuximab can be used in combination with trastuzumab and other anti-HER2 therapies as well as docetaxel and is expected to be used in those patients with metastatic breast cancer who have not received anti-HER2 therapy or chemotherapy. Patuximab (trade name) is a monoclonal antibody. It is the first monoclonal antibody to be called a “HER dimerization inhibitor”. By binding to HER2, it blocks heterodimerization of HER2 with other HER receptors, thereby slowing tumor growth. Patuximab was approved by the FDA on June 8, 2012, for the treatment of HER2-positive metastatic breast cancer. Patuximab was developed by Genentech, which was acquired by Roche Pharmaceuticals in 2009 and patuximab is now in the hands of Roche Pharmaceuticals. A clinical trial enrolling 808 patients with metastatic breast cancer who tested HER2-positive prior to treatment evaluated the safety and efficacy of patuximab. Patients were randomized into two groups: a treatment group receiving patuximab + trastuzumab + docetaxel and a control group receiving trastuzumab + docetaxel + placebo. The study evaluated the progression-free survival (PFS) of patients. The results showed that the median PFS was 18.5 months in the treatment group combined with pertuzumab and 12.4 months in the placebo group. The most common adverse reactions in patients treated with pertuzumab + trastuzumab + docetaxel included diarrhea, hair loss, leukopenia, nausea, malaise, rash and nerve damage (peripheral sensory neuropathy). Trastuzumab, a monoclonal antibody against Her 2, blocks the growth of cancer cells by attaching itself to Her2 to prevent the body’s epidermal growth factor from attaching to Her2, and Herceptin also stimulates the body’s own immune cells to destroy cancer cells. Trastuzumab is a recombinant DNA-derived humanized monoclonal antibody that selectively acts on the extracellular site of human epidermal growth factor receptor-2 (HER2). This antibody is of the IgGl type and contains the human framework region, and the complementary determining region of a murine anti-p185 HER2 antibody that binds to HER-2. The humanized anti-HER2 antibody was produced from mammalian cells (Chinese hamster ovary cells CHO) suspended in sterile medium and purified by affinity chromatography and ion exchange, including a special removal procedure for viral inactivation. The HER2 proto-oncogene or C-erbB2 encodes a single receptor-like transmembrane protein with a molecular weight of 185 kDa that is structurally related to the epidermal growth factor receptor. HER2 overexpression has been observed in 25-30% of patients with primary breast cancer. HER2 gene amplification results in increased HER2 protein expression on the surface of these tumor cells, leading to HER2 receptor activation. Studies have shown that patients with HER2 overexpression tumors have shorter disease-free survival than those without overexpression. HER2 overexpression can be diagnosed by the following methods: immunohistochemical-based evaluation of tumor tissue blocks, ELISA of tissue or plasma samples, or fluorescence in situ hybridization (FISH). Trastuzumab is a potential mediator of antibody-dependent cell-mediated cytotoxic responses (ADCC). In in vitro studies, trastuzumab-mediated ADCC was shown to be produced preferentially in HER2 overexpressing cancer cells than in HER2 non-overexpressing cancer cells.