Performance analysis of Leica Biosystems p16 monoclonal antibody in oropharyngeal squamous cell carcinoma

BackgroundHead and neck squamous cell carcinoma (HNSCC) is the sixth leading cause of cancer death globally, with newly diagnosed oropharyngeal squamous cell carcinoma (OPSCC) cases rising to 54,000 in the US alone in the year 2022. Recently, human papilloma virus (HPV) infection was more prevalent in OPSCC patients than the traditionally known carcinogens such as tobacco or alcohol. HPV 16 is the most common causative HPV strain, which is found in 5-10% of HNSCC patients. HPV 16's E6 and E7 oncoproteins bind and inactivate p53 and retinoblastoma (Rb) tumor-suppressing genes. This causes aberrant over-expression of the cell cycle inhibitor gene, p16, leading to tumorigenesis. Leica Biosystems (LBS) has developed a p16 antibody (6H12 clone) for qualitatively identifying the p16 protein in formalin-fixed paraffin-embedded (FFPE) tissue by immunohistochemical staining. This method comparison study tested the concordance rates between ready-to-use (RTU) LBS p16/LBS RTU p16 antibody and Roche Tissue Diagnostics (RTD) CINtec p16 Histology immunohistochemical (IHC) assays by measuring overall agreement (OA), average positive agreement (APA), and average negative agreement (ANA) rates in 170 OPSCC FFPE cases. Interobserver agreement of the 2 assays and LBS RTU p16 comparison with the standard HPV molecular assays (DNA ISH and PCR) were also assessed. MethodsOne hundred and seventy (170) unique oropharyngeal cancer cases were stained for qualitative analysis by the LBS p16 antibody on BOND III. This assay was compared to Ventana's RTD E6H4 (CINtec) clone on Benchmark XT. A stained core was considered p16 positive if the Histoscore (H score) was >= 140 and negative if H < 140. ResultsAcross the pathologists, the agreement rate between the 2 assays ranged from OA, 98.7 - 98.8%, ANA, 98.8 -98.9%, and APA, 98.6%. For LBS RTU p16, the interobserver agreement was OA, 98.7%, ANA, 98.8%, and APA, 98.6%; while for RTD CINtec p16 assay, the concordance was OA, 98.7%, ANA, 98.8% and APA, 98.6%. In comparison to the HPV molecular testing, DNA ISH, and PCR, across pathologists, LBS p16 clone (LBS RTU p16) showed a concordance rate of 85.8-86.9% and 87.6-88.8%, respectively. ConclusionLBS p16 monoclonal antibody demonstrated high concordance with CINtec p16 IHC assay across all the endpoints, suggesting a potential use of LBS RTU p16 clone in detecting p16 protein in oropharyngeal cancer cases.