Human Epidermal Growth Factor Receptor 2 Testing in Breast Cancer: American Society of Clinical Oncology / College of American Pathologists Clinical Practice Guideline Focused Update

This clinical practice guideline is a focused update of the American Society of Clinical Oncology / College of American Pathologists 2013 guideline on human epidermal growth factor receptor 2 (HER2) testing in breast cancer. Recommendations are provided around what the most appropriate definition is for immunohistochemistry (IHC) 2+, whether HER2 testing should be repeated on surgical specimens if initial core biopsy results are negative, and which invasive cancers should be considered in situ hybridization (ISH) positive. In addition, appropriate diagnostic workup is discussed for invasive cancers based on the HER2 signals present.