Immunohistochemical expression of internal and external ErbB-2 domains in invasive breast cancer

We tested three ErbB-2 monoclonal antibodies (MoAbs) specific to the intracytoplasmic internal domain (clone CB 11) and the extracellular glycosylated peptide domain (clones CBE1 and Tab250) in 351 primary invasive breast carcinomas. ErbB-2 immunodetection allowed us to differentiate three main groups: group 1 (62.7%) lacked both MoAb ErbB-2 domains (erb -/-); group 2 stained for both domains (erb +/+) (26.5%); group 3 stained for the internal domain only (erb +/-) (10.8%). The relationships among these groups and nodal status (N) were statistically significant, with N+ cases reaching the highest value (89.2%) in the erb +/- group. Lack of immunostaining in the external domain thus seems to be associated with increased metastatic spread. At variance analysis the difference in hormonal receptor content between groups 1 and 3 was not significant; while between groups 1 and 2 it was. The growth fraction of groups 2 and 3 was significantly higher than that of group 1. Our results showed that anti-ErbB-2 MoAb clone CB 11 was able to detect a higher number of ErbB-2 expressing cases than the two that are specific for the external domain (clones Tab 250 and CBE1). Due to the strong association between group 3 cases and the highest metastatic potential, this aggressive group could be identified only with the use of an internal-domain specific MoAb CB11, which thus seems to present a better discriminative power as a diagnostic marker in the biopathological characterization of breast carcinoma.