Activation (Tyrosine Phosphorylation) of ErbB-2 (HER-2/neu): A Study of Incidence and Correlation With Outcome in Breast Cancer

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Abstract
PURPOSE: We hypothesize that phosphorylated ErbB-2 (P-ErbB-2, identified by a novel antibody PN2A) may provide either more significant or additional prognostic marker data for breast cancer patients. This study was designed to compare the incidence and prognostic value of ErbB-2 (HER-2/neu) and P-ErbB-2 immunoexpression in archival breast cancer samples. MATERIALS AND METHODS: Eight hundred sixteen invasive breast cancers with a median of 16.3 years of follow-up were immunostained for ErbB-2 (using antibody CB11) and P-ErbB-2 (using antibody PN2A). ErbB-2 and P-ErbB-2 data were compared with clinical, histologic, immunohistochemical, and outcome variables. RESULTS: Of 816 primary breast cancers, 307 (38%) were positive for ErbB-2 and 37 (12% of ErbB-2 positive and 5% of the study population) expressed P-ErbB-2. P-ErbB-2 was not detected in ErbB-2–negative cases (n = 509). ErbB-2 immunohistochemical data were bimodal; patients with ≥ 80% cellular expression had the shortest disease-free and disease-specific survival. P-ErbB-2 was associated with a higher percentage of ErbB-2–positive cells, a higher number of positive lymph nodes, and cellular proliferation. ErbB-2 and P-ErbB-2 were indicators of poor prognosis in node-positive patients in both univariate and multivariate analyses. We found that either P-ErbB-2 expression or high (≥ 80%) ErbB-2 expression provided the most significant prognostic value in node-positive cases by multivariate analyses. There were too few P-ErbB-2–positive cases and events in the node-negative patient group to allow statistical analysis of P-ErbB-2 in that subgroup. CONCLUSION: PN2A immunostaining identified a subset (approximately 12% of ErbB-2–positive breast cancers) with activation (phosphorylation) of the receptor ErbB-2. P-ErbB-2 expression was strongly associated with higher levels of ErbB-2 expression (≥ 80%), although it was not a surrogate. Identification of cases with a high percentage of invasive breast cancer cells expressing ErbB-2 or determination of receptor activation via P-ErbB-2 may provide additional prognostic value in node-positive breast cancers.