Originally published as JCO Early Release 10.1200/JCO.2008.17.3989 on March 2 2009

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Value and Limitations of Measuring HER-2 Extracellular Domain in the Serum of Breast Cancer Patients

From the Royal Marsden Hospital, London, United Kingdom; Sunnybrook and Women's College, Health Science Center, Toronto, Canada; Netherlands Cancer Institute, Amsterdam, the Netherlands; Centre Jean Perrin, Clermont-Ferrand, France; Klinikum Kassel, Kassel, Germany; Tokai University School of Medicine, Kanagawa, Japan; and Westmead Hospital, Westmead, New South Wales, Australia.

Corresponding author: Mitch Dowsett, PhD, Academic Department of Biochemistry, Royal Marsden Hospital, Fulham Rd, London, SW3 6JJ, United Kingdom; e-mail: Mitch.dowsett{at}icr.ac.uk.

The human epidermal receptor-2 (HER-2) is overexpressed or amplified in 15% to 25% of breast cancers. Determination of HER-2 tumor status offers clinically useful information, as it selects patients who may benefit from treatment with trastuzumab, the monoclonal antibody against HER-2. Currently approved methods for HER-2 testing include immunohistochemistry or fluorescent in situ hybridization using tumor tissue. A fragment of HER-2 composed of its extracellular domain (ECD) can also be detected in the serum of some patients with breast cancer. As an easily accessible tumor marker, it could offer additional useful prognostic or predictive information. This review will briefly address the biology of the circulating HER-2 ECD and discuss the evidence to support the role, if any, for measuring HER-2 ECD levels in women with breast cancer. In particular, we focus on the value and limitations of serum ECD in both early and advanced breast cancer in the following clinical contexts: as a marker of HER-2 tumor tissue status; clinical implications of raised levels in women who have a tumor not overexpressing HER-2; as a prognostic indicator and as a predictor of response to treatment; and as a monitoring tool for early recurrence. On the basis of our review of the literature, we conclude that there is currently insufficient evidence to support the use of serum HER-2 ECD in the routine management of individual patients with breast cancer. This conclusion is in agreement with the 2007 American Society of Clinical Oncology guidelines on the use of biomarkers in breast cancer.

Terms in blue are defined in the glossary, found at the end of this article and online at www.jco.org.

Authors' disclosures of potential conflicts of interest and author contributions are found at the end of this article.

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