All persons with invasive breast cancer (early stage or recurrence) should undergo testing for human epidermal growth factor receptor 2 (HER2), and at least one tumor sample should be tested for either HER2 protein expression, using immunohistochemistry (IHC) assay, or for HER2 gene amplification, using in-situ hybridization (ISH) assay.

This recommendation is one of several included in an updated guideline from the American Society of Clinical Oncology (ASCO) and the College of American Pathologists (CAP) regarding HER2 testing in breast cancer. Such testing is performed to identify patients who could benefit from trastuzumab (Herceptin), lapatinib (Tykerb), pertuzumab (Perjeta), T-DM1 (Kadcyla), or other HER2-targeted therapies.

The ASCO/CAP information updates 2007 guidance issued by the two groups. Whereas the earlier version focused on IHC and fluorescence ISH (FISH), the update includes recommendations for bright-field ISH, which is a newer diagnostic technique.

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Antonio C. Wolff, MD, who is the co-chair of the ASCO/CAP HER2 Testing in Breast Cancer Panel and an oncology professor at the Johns Hopkins Kimmel Comprehensive Cancer Center in Baltimore, Maryland, and fellow members of the ASCO/CAP Update Committee devised one set of recommendations for oncologists and one for pathologists. The recommendations are published in ASCO’s Journal of Clinical Oncology and in CAP’s Archives of Pathology & Laboratory Medicine.

Among the key recommendations for oncologists are the following:

• To guide the patient in deciding whether to pursue HER2-targeted therapy, oncologists must request HER2 testing on every primary invasive breast cancer (and on metastatic site, if the cancer is stage 4 and if a specimen is available). Such testing should especially be considered for a patient who previously tested HER2-negative in a primary tumor and presents with disease recurrence with clinical behavior suggestive of HER2-positive or triple-negative disease.

• The oncologist should recommend HER2-targeted therapy if the HER2 test result is positive, if there is no apparent histopathologic discordance with HER2 testing as detailed in the guideline, and if clinically appropriate. Additional HER2 testing may be needed if the oncologist or the pathologist observes an apparent histopathologic discordance after HER2 testing.

• If the initial HER2 test result is equivocal, reflex testing should be performed on the same specimen using an alternative test as specified. The oncologist must delay the decision to recommend HER2-targeted therapy to patients with equivocal test results.

• The oncologist must not recommend HER2-targeted therapy if the HER2 test result is negative and if there is no apparent histopathologic discordance with HER2 testing. If the oncologist or the pathologist does observe such discordance, additional testing may be needed.