Gene protein assay for assessing the HER2 status in breast carcinoma
Human epidermal growth factor receptor 2 (HER2) protein overexpression and/or gene amplification are important prognostic parameters and are biomarkers for targeted anti-HER2 therapy in patients with breast and gastric cancer. Assessing the tumors’ HER2 status requires both immunohistochemical (IHC) and in situ hybridization (ISH) analyses which are routinely performed on separate histological slides in most laboratories. This routine limits the possibility of analyzing the same tumor cell with both methods. The novel gene-protein assay (GPA)1 allows simultaneous demonstration of protein expression and gene status in a single slide combining IHC with dual bright-field ISH technique. Compared to fluorescence ISH technique (FISH), the GPA method provides preserved histology details and preserved signals for archiving, while the FISH method is characterized with less preserved histological details and the signals fade over time. The laboratory turn-around time is also much shorter in case of GPA. The results of GPA are at the same time concordant with FISH results in up to 98%, with chromogen ISH in 100%, and with silver ISH in 96% in related studies while the concordance with IHC alone is lower (76.3% and 93%).2 During the period March 2013 – October 2016, we performed 1616 GPA tests, the vast majority on breast cancer samples; 682 tests were done on selected material from another institution and 934 on our own material. In a consecutive series of 718 non-selected invasive breast carcinomas tested with GPA method at our institution, we found 95% (62/65) of the IHC3+ cases, 24% (21/87) of the IHC 2+ cases, and 1% (5/566) of the IHC0/1+ cases being amplified, while the number of equivocal cases was low 1% (6/718). A TMA study including 589 cases found 95% of IHC 3+, 60% of 2+ and 0.6% of 0/1+ cases being amplified in GPA slides.3 GPA is a robust method of assessing HER2 status, equal to the more established IHC and ISH techniques. It has the advantage of a direct cell-to-cell comparison of protein expression and gene amplification status which opens new perspectives in assessing intratumoral heterogeneity.
1. Nitta H et al. Diagn Pathol 2012 May 30;7:60. doi: 10.1186/1746-1596-7-60.
2. Tot T and the Gene Protein Assay European Working Group members. European Congress of Pathology 2016. 3. Varga S et al. PLOS one August 25, 2014 DOI: 10.1371/journal.pone.0105961
Tibor Tot is associate professor of pathology at the University of Uppsala, Sweden and head the department Pathology & Cytology Dalarna at the County Hospital in Falun, Sweden. The last years he is one of the faculty members in the breast pathology arm of the European School of Pathology, invited faculty member in European School of Radiology, and one of the scientific directors in the European School of Oncology Certificate of Competence in Breast Cancer program. His main fields of interest are breast pathology, colorectal pathology and immunohistochemistry. In addition to more than 90 peer reviewed journal articles and 22 book chapters, he is the author of the book Practical Breast Pathology (Thieme 2002, second edition 2014) and co-author of the Thieme Series on Art and Science of Mammography. He edited two Springer books related to modern breast cancer diagnostics. Dr Tot’s sick lobe theory is a concept gaining more and more acceptance when earliest stages of breast cancer development are considered. He is repeatedly invited lecturer at international and national congresses, symposia, and teaching courses all over the world, member of the Editorial Board of Virchows Archiv, Vojnosanitetski pregled (Belgrade), the Journal of OncoPathology, and the Journal of Solid Tumors, one of the editors of Case Reports in Pathology. He is member of the European Working Group for Breast Cancer Screening Pathology, past chair of the Working Group for Breast Pathology of the European Society of Pathology, and member of the Council of the European Society of Pathology.