Ivkovic-Kapic, Tatjana (56246924300)Tatjana (56246924300)Ivkovic-KapicKnezevic-Usaj, Slavica (6603358705)Slavica (6603358705)Knezevic-UsajMoldvaji, Eva (57209413296)Eva (57209413296)MoldvajiJovanic, Irena (55623723900)Irena (55623723900)JovanicMilovanovic, Zorka (25228841900)Zorka (25228841900)MilovanovicMilentijevic, Maja (7801549028)Maja (7801549028)MilentijevicTatic, Svetislav (6701763955)Svetislav (6701763955)TaticMitrovic, Slobodanka (36017336100)Slobodanka (36017336100)MitrovicStojiljkovic, Miodrag (25959427400)Miodrag (25959427400)StojiljkovicCvetanovic, Ana (55886180500)Ana (55886180500)Cvetanovic2025-07-022025-07-022019https://www.scopus.com/inward/record.uri?eid=2-s2.0-85067674264&partnerID=40&md5=e1823930a401622278197774f5fa1672https://remedy.med.bg.ac.rs/handle/123456789/12745Purpose: The purpose of this study was to assess the immunohistochemistry and chromogenic in situ hybridization (CISH) inter-laboratory consensus between national pathology laboratories in Serbia. Methods: This study was conducted between 2013 and 2016. In 2013, HER2 results were evaluated using two sets of four different breast cancer specimens in five laboratories. A total of 20 immunohistochemistry and 20 CISH cases were tested. In 2014, there were 6 testing rounds, and a total of 24 specimens were analyzed, whereas in 2015 and 2016, seven testing rounds were conducted, with four additional cases (i.e. a total of 28 specimens). In 2014, 2015 and 2016, all institutions performed immunohistochemical analysis only. Results: We found discrepancies in HER2 immunohistochemical (IHC) results in all four surveys. IHC testing resulted in diagnostic discordance between participating centers in two (2/17) cases in 2013, two (2/24) in 2014, four (4/27) cases in 2015 and three cases (3/27) in 2016. The overall agreement among the centers was 79%, 85.5%, 83.5% and 89.4%, respectively. For CISH analyses, the results for 16 (84.2%) of 19 samples were consistent for all participants. Three results were found to be discordant, indicating a misdiagnosis rate of 15.8%. In all the discrepant cases, interinstitutional discordances were related to technical and evaluation issues. Conclusions: Our study highlights the difficulty encountered during HER2 testing using immunohistochemistry and CISH. This also emphasizes the need for rigorous quality control procedures for specimen preparation and analysis. © 2019 Zerbinis Publications. All rights reserved.Breast cancerHER2 testingInter-laboratory consensusQuality control