Abstract
Her‐2/neu overexpression in human breast cancer leads to an aggressive biological behavior and poor prognosis. Although the anti‐Her‐2/neu antibody trastuzumab (Herceptin®) has become a valuable therapeutic option for patients with Her‐2/neu‐overexpressing breast cancer, many patients do not benefit from this therapy. To evaluate the effect of receptor activation on tumor response, we have investigated the phosphorylation status of Her‐2/neu and EGFR in 46 Her‐2/neu‐overexpressing tumor samples from trastuzumab‐treated metastatic breast cancer patients by immunohistochemistry. Activated (p)tyr‐1248 Her‐2/neu was detected in 9 of 46 breast cancers (20%), and activated (p)tyr‐845 and (p)tyr‐1173 EGFR were both present in 6 tumors (13%) while EGFR was present in 16 cases (35%). ptyr‐1248 Her‐2/neu showed a trend to correlate with increased response to trastuzumab (p = 0.063), while ptyr‐845, ptyr‐1173 EGFR and EGFR did not. The presence of ptyr‐1248 Her‐2/neu and ptyr‐845 or ptyr‐1173 EGFR, however, was a strong predictor of both response to trastuzumab‐based treatment (OR = 8.0, p = 0.021 and OR = 8.0, p = 0.021) and clinical benefit (OR = 5.47, p = 0.041 and OR = 6.22, p = 0.028 multivariate logistic regression analysis). Furthermore, ptyr‐845 EGFR and ptyr‐1248 Her‐2/neu were both independent predictors of progression‐free survival (RR = 0.21, p = 0.01 and RR = 0.45, p = 0.026, multivariate analysis). Patients with ptyr‐845 EGFR positive tumors also tended toward increased overall survival (RR = 0.17, p = 0.082). Taken together, we have demonstrated that the determination of activated EGFR improves the utility of ptyr‐1248 Her‐2/neu staining in predicting the clinical outcome of patients undergoing trastuzumab treatment. We hypothesize that the activation state of both Her‐2/neu and EGFR are key determinants for trastuzumab efficacy. © 2005 Wiley‐Liss, Inc.