Quantitative pcr analysis of c-erb B-2 (HER2/neu) gene amplification and comparison with p185(HER2/neu) protein expression in breast cancer drill biopsies

A PCR assay using capillary electrophoresis was designed for the detection of c-erbB-2 gene amplification in alcohol-formalin-acetic acid (AFA)-fixed, paraffin-embedded biopsies from 81 consecutive breast tumors. c-erbB-2 exp ression was analyzed in the same samples using immuno-histochemistry (IHC). In the competitive PCR assay, a single pTag plasmid containing a 4-nucleot ide (nt)-deleted copy of a 124-nt sequence of c-erbB-2 and a l-nt-deleted c opy of a 120-nt sequence of GAPDH was co-amplified with genomic DNA extract ed from 3 10-mu m-thick tissue sections of the tumor biopsy. The percentage of tumor cells in the biopsy specimen and the percentage of tumor cells st ained with the membrane anti-c-erbB2 monoclonal antibody CB II were recorde d by a single pathologist on 2 consecutive sections. Among 81 consecutive t umor biopsies assayed by PCR, 21 (26%) displayed unequivocal c-erbB-2 ampli fication (actual gene copy number, AGCN > 4), 47 (58%) displayed no c-erbB- 2 amplification (AGCN less than or equal to 2) and 7 (9%) could not be anal yzed due to an insufficient amount of DNA. Six samples (7%) were considered inconclusive since the percentage of tumor cells was <20%, Analysis of c-e rbB-2 expression by IHC showed that among the 21 amplified specimens 15 dis played strong staining, while all non-amplified samples (47) displayed no o r only weak staining. The concordance of the 2 techniques was 91%. We concl ude that c-erbB-2 gene amplification can be accurately quantitated by compe titive PCR performed on small, fixed and embedded tumor samples. (C) 1999 W iEey-Liss, Inc.