[Development of HER2-specific humanized antibody Herceptin (trastuzumab)].

HER2 is a member of the human epidermal growth factor receptor family, possessing protein kinase activity in its cytoplasmic domain. There were evidences indicating that (1) amplification of HER2/neu gene and HER2 protein over-expression in tumor cells was observed in 25-30% of human breast cancer and (2) amplification of HER2/neu correlated with poor prognosis, including shorter disease-free and overall survival. These evidences suggested HER2 was a promising candidate for novel molecular targets of breast cancer therapy. Herceptin is a recombinant humanized monoclonal antibody generated by Genentech, Inc. for the treatment of HER2 over-expressed/HER2 gene amplified metastatic breast cancer (MBC). Preclinical studies demonstrated that the antibody had anti-tumor activity in vivo and in vitro, and additive or synergistic enhancement of anti-tumor activity of the antibody was observed in combination with various anti-tumor agents in mouse models. In clinical studies, apparent extension of overall survival was observed in HER2 overexpressing MBC patients. Herceptin is the first anticancer drug whose use as a treatment for MBC patients is decided based on the status of the HER2 gene amplification/HER2 protein over-expression. The development and standardization of HER2 test were a key strategy in clinical development of this drug, since appropriate selection of patients with HER2 over-expression was the essential point for success.