[Clinical evaluation of ErbB-2 protein in tissue extract using an enzyme immuno assay (ErbB-2 EIA "Nichirei")]

ErB-2 protein levels in breast cancer tissue extracts were determined by an enzyme immuno assay (ErbB-2 EIA "Nichirei") using anti-c-erbB-2 monoclonal antibodies, and compared with the c-erbB-2 gene amplification detected by dot blot hybridization or differential PCR, and with the overexpression detected by immunostaining. The positivities of c-erbB-2 gene amplification and overexpression in breast cancer tissues were 25.0% (14/56) and 39.3% (46/117), respectively. The cut-off values of the Erb B-2 protein in tissue extract by EIA were set at 18.0 ng/mg-protein for gene amplification and 10.4 ng/mg-protein for overexpression, respectively, from the data of breast cancer tissues which were negative for c-erbB-2 gene. The accuracy of the ErbB-2 protein levels in tissue extract with c-erbB-2 gene amplification and overexpression were 90.6% and 79.2% using these cut-off values respectively. The result of c-erbB-2 gene amplification, overexpression, and ErbB-2 protein levels were significantly correlated with negative estrogen receptor (ER) and progesterone receptor (PgR) status in tissue cytosol fraction. These results indicate that measurement of ErbB-2 protein in tissue extract is useful to estimate the c-erbB-2 gene amplification and/or overexpression in breast cancer tissues.