Protein overexpression and gene amplification of c-erbB-2 in breast carcinomas: a comparative study of immunohistochemistry and fluorescence in situ hybridization of formalin-fixed, paraffin-embedded tissues.

We evaluated 173 consecutive breast carcinomas for c-erbB-2 using a combination of immunohistochemistry (IHC) with a commercial polyclonal antibody (Nitirei) and dual-color fluorescence in situ hybridization (FISH) using the c-erbB-2-specific probe and the chromosome 17 centromere-specific probe from Vysis (Downers Grove, IL) and compared the results with the histologic characteristics of intraductal spread, cancer invasion, and intratumoral heterogeneity. With correction for chromosome 17 copy number, c-erbB-2 amplification was observed in 26 tumors (13.5%): high-level amplification in 23 tumors, and low-level amplification in 3. The gene amplification was positively correlated with c-erbB-2 protein overexpression, defined as 2+ or 3+ immunostaining, on a case-by-case basis (P < .000001). All 3+ immunostaining tumors (19 tumors) showed high-level amplification, although gene amplification was found in only 5 of 27 2+ immunostaining tumors. Although the rates of overexpression and gene amplification did not differ in ductal carcinomas in situ and invasive carcinomas (P = .46 and .53, respectively), they were significantly higher in invasive carcinomas with intraductal spreading (P < .0001). Intratumoral heterogeneity of c-erbB-2 amplification was found in only 1 case; however, in 17 invasive carcinomas, intraductal components expressed c-erbB-2 more intensely than invasive components. We conclude that in breast carcinomas, c-erbB-2 overexpression occurs mostly in tumors with high-level gene amplification, and such overexpression appears to endow carcinoma cells with the capacity for intraductal spreading. The best method for detecting breast carcinomas with c-erbB-2 aberrations using archival tissues is to screen cases by IHC; however, follow-up FISH assays are indispensable for excluding false-positive results. Copyright 2002 by W.B. Saunders Company