Potential Clinical Utility of Serum HER-2/neu Oncoprotein Concentrations in Patients with Breast Cancer

receptor protein are indicators of a more aggressive form of breast cancer. HER-2/neu status guides Herceptin therapy, specifically directed to the extracellular domain (ECD) of the HER-2/neu oncoprotein. The HER-2/neu ECD is shed from cancer cells into the circulation and is measurable by immunoassay. Methods: We performed a systematic review of the peer-reviewed literature on circulating ECD with re-spect to prevalence, prognosis, prediction of response to therapy, and monitoring of breast cancer. Results: The prevalence of increased ECD in patients with primary breast cancer varied between 0 % and 38% (mean, 18.5%), whereas in metastatic disease the range was from 23 % to 80 % (mean, 43%). Some women with HER-2/neu-negative tumors by tissue testing develop increased ECD concentrations in metastatic disease. Increased ECD has been correlated with indicators of poor prognosis, e.g., overall survival and disease-free survival. Increased ECD predicts a poor response to hormone therapy and some chemotherapy regimens but can predict improved response to combinations of Her-ceptin and chemotherapy. Many studies support the value of monitoring ECD during breast cancer progres-sion because serial increases precede the appearance of metastases and longitudinal ECD changes parallel the clinical course of disease. Conclusions: The monitoring of circulating HER-2/neu ECD provides a tool for assessing prognosis, for predict-ing response to therapy, and for earlier detection of disease progression and timely intervention with appro-priate therapy. © 2003 American Association for Clinical Chemistry The activation and overexpression of cellular oncogenes has been considered to play an important role in the development of human cancer (1). An important member of the oncogene family is the growth factor receptor known as human epidermal growth factor receptor-2 (HER-2)8 (2), which is also referred to as HER-2/neu or c-erbB-2. HER-2/neu is structurally and functionally re-lated to the v-erbB retroviral oncogene (3) and is part of the HER family, which also includes HER-1, or epiderma