HER2 Status and Benefit from Adjuvant Trastuzumab in Breast Cancer

To the Editor: Trastuzumab, an antibody against the protein product of the human epidermal growth factor receptor type 2 ( HER2 ) gene, improves progression-free survival and overall survival when added to chemotherapy in patients with metastatic breast cancer. 1 Initial trials enrolled patients with tumors that had a staining intensity of 2+ or 3+ for HER2 on immunohistochemical analysis, but in subsequent studies, the benefit was limited to tumors with HER2 amplification as determined by fluorescence in situ hybridization (FISH). Trastuzumab also improves disease-free survival and overall survival in the adjuvant setting. 2 On the basis of its mechanism of action, . . .