Probes for P16

Routine testing for p16 immunohistochemistry (with selective HPV-specific test use) has been recommended for clinical practice in oropharyngeal squamous cell carcinoma (OPSCC). Data suggests that the E6H4 clone performs best for this purpose, yet no studies have evaluated the optimal antibody concentration for OPSCC testing. We evaluated three concentrations (undiluted, 1:5, and 1:10) of the primary antibody solution for E6H4 using tissue microarrays from a cohort of 199 OPSCC patients with a > 70% staining cutoff for positivity. Concordance was evaluated using percent agreement and Cohen's kappa. The concentrations were evaluated for sensitivity and specificity using high risk HPV RNA in situ hybridization (RNA-ISH) and also correlated with Kaplan-Meier overall survival analysis. Inter-rater agreement was very high between p16 results at each concentration and also with RNA in situ hybridization (p < 0.0001 for all). Agreement between p16 undiluted and 1:5 dilution (agreement 98.2%; Kappa 0.943; p < 0.0001) was very high and between p16 undiluted and 1:10 dilution (agreement 79.2%; Kappa 0.512; p < 0.0001) much lower. Intensity of the staining did decrease with the 1:5 and 1:10 dilutions compared to undiluted, but not in a manner that obviously would change test interpretation or performance. Results suggest that the E6H4 antibody performs well at dilutions of up to 1:5 fold with a minor decrease in staining intensity, minimum loss of sensitivity, and no loss of specificity in OPSCC patients. This could result in reagent and cost savings.

Background

Oropharyngeal cancers associated with high-risk type human papillomavirus (HR-HPV) infection have better prognosis than virus negative cancers. Similarly, the HPV status in laryngeal cancer (LC) may be associated with better outcome.

Methods

Samples from 88 patients with LC were investigated using the polymerase chain reaction (PCR) and p16 immunohistochemistry for HR-HPV analysis. The cut-off point for p16 overexpression was diffuse (≥75%) tumor expression with at least moderate (+ 2/3) staining intensity.

Results

The 5-year cumulative survival (CS) rate was 80.7% in all patients with LC. According to a combination of HR-HPV DNA status and p16 overexpression, subjects with LC were divided into four groups: HR-HPV DNA-positive/p16 overexpression-positive (n = 5, 5.7%; CS = 100%), HR-HPV DNA-positive/p16 overexpression-negative (n = 11, 12.5%; CS =81.8%), HR-HPV DNA-negative/p16 overexpression-positive (n = 0), and HR-HPV DNA-negative/p16 overexpression-negative (n = 72, 81.8%; CS = 79.5%). HR-HPV DNA-positive/p16-positive cases tended to have integrated HPV infection and high viral load, compared with HR-HPV DNA-positive/p16 overexpression-negative cases.

Conclusions

LC patients with HPV infection and high levels of p16 expression might have an improved survival outcome; however, it is necessary to recruit additional LC cases with HPV infection to determine the definitive characteristics of HPV-mediated LC and estimate survival outcome. These results may contribute to the development of a useful method for selecting patients with a potentially fair response to treatment and ensure laryngeal preservation.

Objectives

Evaluation of human papillomavirus (HPV) status in oropharyngeal squamous cell carcinoma (OPSCC) has become increasingly important for prognostication and clinical trial enrollment. This assessment is confounded in OPSCCs that are p16 positive by immunohistochemistry (IHC) but HPV negative by DNA in situ hybridization (DISH). This study evaluates whether E6/E7 mRNA in situ hybridization (RISH) can detect transcriptionally active HPV in these problematic cases.

Materials and methods

Eighty-two head and neck squamous cell carcinoma cases that had previously undergone p16 IHC and HPV DISH were evaluated with two RISH platforms and a second-generation DISH probe. The study included 21 p16+/DISH+ concordant cases, 19 p16−/DISH− concordant cases, and 42 p16+/DISH− discordant cases.

Results

RISH identified E6/E7 mRNA in 37 (88%) p16+/DISH− cases, 21 (100%) p16+/DISH+ cases, and 0 (0%) p16−/DISH− cases. RISH signals were clearly visible at low to medium magnification in 97% of positive cases, facilitating almost-perfect inter-observer reproducibility. The performance of the manual and automated RISH platforms were equivalent (kappa = 0.915). Only 29% of carcinomas that demonstrated E6/E7 mRNA transcriptional activity were positive using the 2nd generation DISH probe.

Conclusions

HPV RISH is a highly sensitive and specific platform that can clarify the HPV status of those perplexing OPSCCs that are p16 positive by IHC but HPV negative by DISH. Moreover, it is easy to interpret, readily adaptable to the clinical laboratory, and provides direct evidence of HPV transcriptional activity. E6/E7 RISH should be considered as a first-line platform for determination of HPV status in OPSCCs.

HPV-related and HPV-unrelated oropharyngeal squamous cell carcinomas are two distinct entities according to the Union for International Cancer Control, with a better prognosis conferred to HPV-related oropharyngeal squamous cell carcinomas. However, variable clinical outcomes are observed among patients with p16 positive oropharyngeal squamous cell carcinoma, which is a surrogate marker of HPV infection. We aimed to investigate the prognostic value of RNA CISH against E6 and E7 transcripts (HPV RNA CISH) to predict such variability. We retrospectively included 50 histologically confirmed p16 positive oropharyngeal squamous cell carcinomas (p16 positive immunostaining was defined by a strong staining in 70% or more of tumor cells). HPV RNA CISH staining was assessed semi-quantitatively to define two scores: RNA CISH “low” and RNA CISH “high”. Negative HPV RNA CISH cases were scored as RNA CISH “low”. This series contained 29 RNA CISH low cases (58%) and 21 RNA CISH high cases (42%). Clinical and pathologic baseline characteristics were similar between the two groups. RNA CISH high staining was associated with a better overall survival in both univariate and multivariate analyses (p = 0.033 and p = 0.042, respectively). Other recorded parameters had no prognostic value. In conclusion, HPV RNA CISH might be an independent prognostic marker in p16 positive oropharyngeal squamous cell carcinomas and might help guide therapeutics.