Accurate identification of HER2-positive patients is essential for superior outcomes with trastuzumab therapy.

PURPOSE/OBJECTIVES To review the clinical significance, methods of testing, and outcomes of trastuzumab (Herceptin) treatment for HER2 gene amplification and HER2 protein overexpression in breast cancer. DATA SOURCES Published articles and abstracts, online resources, a clinical handbook, and product information. DATA SYNTHESIS HER2 gene amplification or HER2 protein overexpression can be found in 20%-25% of breast cancers and is important pathogenic and prognostic information. HER2 also predicts patient response to trastuzumab. Patients with HER2-positive metastatic breast cancer benefit from trastuzumab whether selected by immunohistochemistry, which measures the HER2 protein, or fluorescence in situ hybridization (FISH), which measures the HER2 oncogene. However, patients who are identified accurately as HER2 gene-amplified by FISH derive the greatest benefit. CONCLUSIONS Accurate testing is crucial for appropriate identification of patients for trastuzumab therapy. FISH is the most reproducible and accurate method. IMPLICATIONS FOR NURSING Education regarding HER2 testing and trastuzumab helps patients to make informed decisions and facilitates active participation in their care as well as enhances dialogue with physicians.