Reliability and Discriminant Validity of HER2 Gene Quantification and Chromosome 17 Aneusomy Analysis by Real-Time PCR in Primary Breast Cancer

Abstract

There is an increasing demand for the evaluation of HER2 status in breast cancer. In this study, sections from fixed tissues and triton extracts of tissue homogenates were obtained from 163 malignant breast tumors and analyzed in parallel using immunohistochemistry combined with fluorescence in situ hybridization, as gold standard tests, and an ELISA test (c-erbB2/c-neu Rapid Format ELISA, Oncogene Research Products, USA). Tumor DNA was employed to evaluate two quantitative PCR methods: the HER2/neu DNA Quantification Kit (Roche Diagnostics GmbH, Germany), which uses the gastrin chromosome 17 reference gene, and our recently developed Oncolab qPCR assay, where both a chromosome 17 gene (somatostatin receptor type II (SSTR2)) and a non-chromosome 17 reference gene (glyceraldehyde-3-phosphate deshydrogenase (GAPDH)) were used to detect an increase in HER2 gene copy number and to evaluate the aneusomy of chromosome 17, respectively. By IHC/FISH and ELISA, HER2 was overexpressed in 27 (16.6%) and 24 (14.7%) samples, respectively. With the Roche and Oncolab qPCR assays, 29 (17.8%) samples showed a ratio of HER2/gastrin ≥2.0 and 26 (16.0%) showed a ratio of HER2/SSTR2 ≥ 2.0, respectively. In samples presenting HER2/SSTR2 <2.0 and HER2/GAPDH ≥2.0, which was indicative of a chromosome 17 polysomy, we observed a modest increase in HER2 protein expression. Complete agreement between the four methods for HER2 status determination was obtained for 154 (94.5%) samples. Overall, these results demonstrate that quantitative PCR is a reliable method for analyzing HER2 status and chromosome 17 polysomy.