A practical guide to HER2 testing

Nurses are becoming increasingly involved in providing information about the full range of medical care to patients. With the identification of increasing numbers of prognostic factors in cancer, this role is extending to include testing for these factors. HER2 status has prognostic and predictive value in breast cancer and the receptor is a target for specific therapies. To identify patients who might benefit from more aggressive treatment regimens or new therapeutic options, it is vital that HER2 abnormalities are accurately measured. A variety of techniques have been developed to measure HER2 overexpression or amplification, including fluorescence in situ hybridization, immunohistochemistry, polymerase chain reaction and enzyme-linked immunosorbent assay. To date, no one test has been accepted as standard and pathology laboratories are using different tests. This has implications for the interpretation of results, which in turn has implications for the widespread use of HER2 testing. This article describes the various tests available for the measurement of HER2, identifies the features of the ideal HER2 test and which test currently best fits these criteria, and considers whether HER2 status should be a routine part of the clinical evaluation of breast cancer patients. Important information that nurses should consider when providing information on HER2 testing to patients is highlighted.