Concordance in judgments among c-erbB-2 (HER2/neu) overexpression detectedby two immunohistochemical tests and gene amplification detected by Southern blot hybridization in breast carcinoma

We compared the c-erbB-2 protein overexpression status detected by the Herc epTest(TM) (DAKO A/S, Grostrup, Denmark) with another conventional immunohi stochemistry system using an anti-c-erbB-2 rabbit polyclonal antibody (Nich irei Co., Tokyo, Japan) and with the c-erbB-2 gene amplification status det ected by Southern blot hybridization in 101 surgically resected breast carc inomas. According to the criteria for overexpression, recommended by the ma nufacturer, c-erbB-2 overexpression by HercepTest(TM) was detected in 24 ca ncers (24%), comprising six score-2 tumors and 18 score-3 tumors. The level of agreement in judgment of the HercepTest(TM), among three independent ob servers, 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 HercepTest(TM) scores of 2 -3 was 89% and 90%, respectively. In the score-3 cases by Hercep Test(TM) o nly, the concordance rates with overexpression by Nichirei's immunohistoche mistry and with gene amplification were slightly higher, 94% and 93%, respe ctively. Score-2 cases by HercepTest(TM) were mostly judged as negative ove rexpression by Nichirei's antibody and as no amplification by Southern blot hybridization. The present results showed that HercepTest(TM) score-3 dete cted c-erbB-2 overexpression almost optimally as well as the conventional m ethods and the score-3 breast carcinomas had clinical and biological implic ations. Further examination would be necessary to decide the significance o f breast cancers of HercepTest(TM) score 2.