In addition, Herceptin synergizes with Pertuzumab, a humanized monoclonal antibody against an epitope of the extracellular domain of HER2 that is distinct from the target sites for Herceptin [8] and increases progression-free survival in metastatic HER2+ breast cancer by 6 months, which is beyond that observed by either agent alone. Here, ERBB2 is linked to breast cancer.