Background
The diagnostic standard for detection of high-risk human papillomavirus (HPV) in oropharyngeal carcinomas has been a two-stage algorithm: p16 immunohistochemistry (IHC) followed by HPV detection by molecular approach (e.g DNA in situ hybridisation (ISH)) in p16 equivocal or positive cases. However, using this approach, a discordant subset of p16 IHC +ve/HPV DNA ISH -ve cases was noted. This study aims to investigate these discrepancies and evaluate an RNA in situ hybridisation test as an alternative to the two-stage algorithm for use in routine diagnostics.
Design: 36 OPCs were tested for the presence of HPV using p16 IHC, HPV DNA ISH, and the new RNA ISH assay (RNAScope®). The study includes p16+/DNA ISH+ (N=16), p16-/DNA ISH- (N=7) and p16+/DNA ISH- discordant cases (N=13).
Results: RNA ISH test detects HPV in 5/13 (38%) p16+/DNA ISH- discordant oropharyngeal cases, 16 (100%) p16+/DNA ISH+ cases, and in 0 (0%) p16-/DISH- cases. There is strong agreement between p16 IHC and RNA ISH (k=0.85), compared to score of k=0.76 for p16 IHC and DNA ISH.
Conclusion: By utilising the RNAScope® assay, the number of discordant cases was significantly reduced. This highly sensitive and specific qualitative method for HPV detection in fixed paraffin embedded tissue (biopsy or cell block) has been validated for use in the SJH routine diagnostic histopathology laboratory.
Giuseppa Castriciano1,2, Esther O’Regan1-4
1 Department of Histopathology, St. James’s Hospital, Dublin
2 Trinity St. James’s Cancer Institute, Dublin
3 Division of Oral & Maxillofacial Surgery, Oral Medicine & Oral Pathology, Trinity College, Dublin
4 Discipline of Histopathology, School of Medicine, Trinity College Dublin