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HER2 Testing to Manage Patients With Breast Cancer or Other Solid Tumors

HER2 Testing to Manage Patients With Breast Cancer or Other Solid Tumors

Evidence Reports/Technology Assessments - Agency for Healthcare Research and Quality (US)

Version: November 2008

Introduction

The human epidermal growth factor (EGF) receptor-2 (HER2; also referred to as HER2/neu and as ERBB2) gene, located at position 17q12 on chromosome 17, is amplified (i.e., gene copy number greater than 2) and/or the HER2 protein is overexpressed (i.e., cell membrane has excess of HER2 protein molecules compared to normal cells) in approximately 18 to 20 percent of breast cancer cases (Owens, Horten, and Da Silva, 2004; Yaziji, Goldstein, Barry, et al., 2004; Wolff, Hammond, Schwartz, et al., 2007a; Slamon, Clark, Wong, et al., 1987; Hanna, O'Malley, Barnes, et al., 2007). Amplification and/or overexpression of HER2 have been associated with increased tumor aggressiveness and poor prognosis. The HER2 gene is one of four (HER1 through HER4) in the EGF receptor gene family; each codes for a membrane-spanning protein that can form homodimers and heterodimers and functions in signal transduction. All but HER2 bind (EGF or another) ligand outside the cell, and all but HER3 have enzymatic activity that phosphorylates tyrosine residues in proteins (i.e., tyrosine kinase activity) and that is activated by ligand binding. Ligand-activated tyrosine kinase initially phosphorylates tyrosine residues of the receptor's intracellular domain, and subsequently can phosphorylate tyrosine residues of other intracellular proteins. HER2 also is overexpressed in varying proportions of other epithelial malignancies such as ovarian, thyroid, lung, salivary gland/head and neck, stomach, colon and prostate cancers (Baselga and Mendelsohn 1994; Blank, Chang, and Muggia, 2005; Gross, Jos, and Agus, 2004). Table 1 provides a listing of the estimated new cases and deaths in the U.S. for these cancers in 2008.

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