Retrospective population-based comparison of HER2 immunohistochemistry and fluorescence in situ hybridization in breast carcinomas: Impact of 2007 American society of clinical oncology/college of American pathologists criteria

摘要

Context.-In 2007 the American Society of Clinical Oncology/College of American Pathologists made new recommendations for HER2 testing and redefined HER2 positivity. Objective.-To analyze results from simultaneous HER2 testing with immunohistochemistry and fluorescence in situ hybridization (FISH) in 2590 invasive breast carcinomas between 2002 and 2010, using 2 scoring systems. Design.-Cases from between 2002 and 2006 were scored by using original US Food and Drug Administration criteria (N=1138) and those from between 2007 and 2010 were evaluated according to American Society of Clinical Oncology/College of American Pathologists criteria (N = 1452). Concordance between testing methods and clinicopathologic associations were determined. Results.-Overall concordance between immunohistochemistry/ FISH in the 9-year period was 96.2 (j=0.82), and positive concordance was lower. After 2007, the proportion of HER2/neu-positive and HER2/neu-negative cases was not significantly changed when using immunohistochemistry (10.5 versus 8.9, P = .22 and 69.4 versus 63, P = .13, respectively), but the number of equivocal cases was higher (19.9 versus 28, P , .001). While the proportion of negative cases by FISH remained unchanged after 2007 (86.5 versus 88.2, P = .76), the number of positive cases was lower (13.4 versus 9.2, P < .001). In addition, 38 cases (2.6) were FISH equivocal, 16 of which were also equivocal by immunohistochemistry. Overall, immunohistochemistry/FISH concordance was 95.9 between 2002 and 2006 (j = 0.82) and 96.4 after 2007 (j = 0.82). However, an approximately 13 lower positive assay concordance was noted in the last period. Conclusions.-Application of American Society of Clinical Oncology/College of American Pathologists recommendations is associated with comparable overall immunohistochemistry/FISH concordance, reduced positive concordance, and increased equivocal results.