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

Abstract We evaluated 173 consecutive breast carcinomas for c- erb B-2 using a combination of immunohistochemistry (IHC) with a commercial polyclonal antibody (Nitirei) and dual-color fluorescence in situ hybridization (FISH) using the c- erb B-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- erb B-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 P =.46 and.53, respectively), they were significantly higher in invasive carcinomas with intraductal spreading ( P erb B-2 amplification was found in only 1 case; however, in 17 invasive carcinomas, intraductal components expressed c- erb B-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- erb B-2 aberrations using archival tissues is to screen cases by IHC; however, follow-up FISH assays are indispensable for excluding false-positive results. HUM PATHOL 33:21-28. Copyright © 2002 by W.B. Saunders Company