We compared the c-erbB-2 protein overexpression status detected by the HercepTestTM (DAKO A/S, Grostrup, Denmark) with another conventional immunohistochemistry system using an anti-c-erbB-2 rabbit polyclonal antibody (Nichirei Co., Tokyo, Japan) and with the c-erbB-2 gene amplification status detected by Southern blot hybridization in 101 surgically resected breast carcinomas. According to the criteria for overexpression, recommended by the manufacturer, c-erbB-2 overexpression by HercepTestTM was detected in 24 cancers (24%), comprising six score-2 tumors and 18 score-3 tumors. The level of agreement in judgment of the HercepTestTM, among three independent observers, was excellent (kappa = 0.845). C-erbB-2 overexpression by Nichirei's antibody and c-erbB-2 gene amplification were detected in 21% and 16% of cases, respectively, and their concordance with HercepTestTM scores of 2-3 was 89% and 90%, respectively. In the score-3 cases by Hercep TestTM only, the concordance rates with overexpression by Nichirei's immunohistochemistry and with gene amplification were slightly higher, 94% and 93%, respectively. Score-2 cases by HercepTestTM were mostly judged as negative overexpression by Nichirei's antibody and as no amplification by Southern blot hybridization. The present results showed that HercepTestTM score-3 detected c-erbB-2 overexpression almost optimally as well as the conventional methods and the score-3 breast carcinomas had clinical and biological implications. Further examination would be necessary to decide the significance of breast cancers of HercepTestTM score 2.
HercepTestTM (DAKO A/S, Glostrup, Denmark) is an immunohistochemical assay that detects HER2/neu gene products, and evaluates the overexpression status of the HER2/neu protein in determining eligibility for the Trastuzumab (HerceptinR, Genentech, San Francisco, CA, USA) therapy. However, practically, interobserver variability of the HER2/neu interpretation of the immunostained results has caused marked disagreement with regard to the intensity of tumor staining. In this study, we quantitated HER2/neu expression by image analysis, and applied this analyzing system to help to minimize interobserver variability of the interpretation of the HercepTestTM. All the immunostained results were scored semiquantitatively on a range of 0 to 3+ in accordance with the criteria described as per the manufacturer's instructions, and quantitatively evaluated using an image analyzing system with image processing software. Among the 92 cases, 15 were scored as 3+, six were 2+, and 32 were 1+ under intraobservers agreement. When the cases were quantitated, a high correlation was shown between the signal area extracted by image analysis and the corresponding score of staining intensity with the HercepTestTM. By converting the quantitatively extracted data into a scoring system based upon the criteria, the outcome demonstrated a strong concordance with the scoring data obtained from immunostaining. The results indicated that a quantitative scoring system performed by simple image analysis may provide to improve interobserver agreement of the interpretation of the HercepTest TM in clinical practice.