RESUMO
UNLABELLED: The human epidermal growth factor receptor 2 (HER2, also known as erbB2) gene is involved in signal transduction for cell growth and differentiation. It is a cell surface receptor tyrosine kinase and a proto-oncogene. Overexpression of HER2 is of clinical relevance in breast cancer due to its prognostic value correlating elevated expression with worsening clinical outcome. At the same time, HER2 assessment is also of importance because successful anti-tumor treatment with Herceptin® is strongly correlated with HER2 overexpression in the tumor (approximately 30% of all breast tumors overexpress HER2). In a comprehensive national study, Wolff et al. [1] state that "Approximately 20% of current HER2 testing may be inaccurate" which underscores the importance of developing more accurate methods to determine HER2 status. Droplet Digital™ PCR (ddPCR™) has the potential to improve upon HER2 measurements due to its ability to quantitate DNA and RNA targets with high precision and accuracy. Here we present a study which investigates whether ddPCR can be used to assess HER2 transcript levels in formalin-fixed paraffin embedded (FFPE) human breast tumors and whether these ddPCR measurements agree with prior assessments of these same samples by pathologists using immunohistochemistry (IHC) and in some cases fluorescence in situ hybridization (FISH). We also determined the copy number of HER2 in these samples as compared to the CEP17 reference gene. RESULTS: Clinical FFPE samples were successfully studied using ddPCR and compared to results from standard FISH and IHC methodology. The results demonstrate that ddPCR can rank order the samples in complete agreement with the current standard methods and that ddPCR has the added benefit of providing quantitative results, rather than relying on the expert skill of a seasoned pathologist for determination.
Assuntos
Neoplasias da Mama/metabolismo , Expressão Gênica , Técnicas de Diagnóstico Molecular/normas , Reação em Cadeia da Polimerase/normas , Receptor ErbB-2/genética , Centrômero/genética , Feminino , Fixadores/química , Formaldeído/química , Dosagem de Genes , Humanos , Imuno-Histoquímica , Hibridização in Situ Fluorescente , Inclusão em Parafina , Proto-Oncogene Mas , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Receptor ErbB-2/metabolismo , Padrões de ReferênciaRESUMO
For the analysis of cancer, there is great interest in rapid and accurate detection of cancer genome amplifications containing oncogenes that are potential therapeutic targets. The vast majority of cancer tissue samples are formalin fixed and paraffin embedded (FFPE) which enables histopathological examination and long term archiving. However, FFPE cancer genomic DNA is oftentimes degraded and generally a poor substrate for many molecular biology assays. To overcome the issues of poor DNA quality from FFPE samples and detect oncogenic copy number amplifications with high accuracy and sensitivity, we developed a novel approach. Our assay requires nanogram amounts of genomic DNA, thus facilitating study of small amounts of clinical samples. Using droplet digital PCR (ddPCR), we can determine the relative copy number of specific genomic loci even in the presence of intermingled normal tissue. We used a control dilution series to determine the limits of detection for the ddPCR assay and report its improved sensitivity on minimal amounts of DNA compared to standard real-time PCR. To develop this approach, we designed an assay for the fibroblast growth factor receptor 2 gene (FGFR2) that is amplified in a gastric and breast cancers as well as others. We successfully utilized ddPCR to ascertain FGFR2 amplifications from FFPE-preserved gastrointestinal adenocarcinomas.