Immunohistochemical Study on Overexpression of c‐erbB‐2 Protein in Human Breast Cancer: Its Correlation with Gene Amplification and Long‐term Survival of Patients

Using a polyclonal antibody monospecific to the c‐erbB‐2 oncogene product, an immunohistochemical study on the expression of c‐erbB‐2 protein was performed in formalin‐fixed, paraffin‐embedded tissue sections from 176 primary breast carcinomas in which amplification of the c‐erbB‐2 gene had been detected in 28 cases. Expression of the c‐erbB‐2 protein was detected in 44 cases (25%), being strongly positive in 27 (15%) and weakly positive in 17 (10%). All cases with amplification of c‐erbB‐2 showed positive staining of its protein. There were only four cases in which c‐erbB‐2 was strongly expressed without amplification of the gene. In the group showing strongly positive staining, both overall and disease‐free survival were significantly poorer than in the remainder of the cases. Using Cox's regression model analysis, overexpression of c‐erbB‐2 protein was demonstrated to be an effective prognostic factor independent of nodal status or tumor size.