Current HER2 Testing Recommendations and Clinical Relevance as a Predictor of Response to Targeted Therapy

Clinical decision-making in the treatment of breast cancer depends on an accurate determination and understanding of human epidermal growth factor receptor 2 (HER2) status. The guidelines for HER2 testing were recently updated in late 2013, but limitations continue to exist in the interpretation and clinical application of results when the tumor specimens do not fall neatly into positive or negative categories with immunohistochemistry and fluorescence in situ hybridization testing. The issues, including discordance between pathologists or laboratories, polysomy, and genetic heterogeneity, present challenging situations that are difficult to translate into clinical significance. The present review discussed the changes in the updated American Society of Clinical Oncology/College of American Pathologists guidelines, the clinical relevance of complex issues in HER2 testing, and the implications of the results on the response to HER2-targeted therapies. Great advances have been made in the treatment of HER2-positive breast cancer; however, the challenge remains to determine the best testing analysis that will identify patients who will benefit the most from these therapies.