Identification of transcriptionally active HPV infection in formalin-fixed, paraffin-embedded biopsies of oropharyngeal carcinoma.

Human papillomavirus (HPV) oncogenic activity is the result of viral oncogene E6 and E7 expression in infected cells. Oncogene expression analysis is, however, not part of the routine diagnostic evaluation of HPV-associated oropharyngeal squamous cell carcinoma (OPSCC) since it requires fresh tumor tissue. We compared the diagnostic accuracy of several methods commonly employed for HPV characterization in OPSCC with the results of the newly available HPV E6/E7 mRNA in situ hybridization (ISH) on formalin-fixed, paraffin-embedded biopsy samples, in order to establish if the latter should be introduced in the diagnostic routine to increase accuracy when fresh tissue is not available. p16 immunostain, DNA ISH for high-risk HPV genotypes, SPF LiPA amplification and genotyping, and HPV16 E6 amplification were performed on 41 consecutive OPSCC samples. Twenty (48.7%) cases were positive by mRNA ISH; sensitivity and specificity were 100% and 90% for p16, 90% and 100% for DNA ISH, 70% and 76% for SPF10 LiPA, 90% and 76% for E6 amplification. A diagnostic algorithm considering p16 immunostain as first step followed by either high-risk HPV DNA ISH or HPV16 E6 amplification in p16-positive cases correctly characterized 90% of mRNA-positive and all mRNA-negative cases; combining the 3 tests correctly identified all cases. While no stand-alone test was sufficiently accurate for classifying HPV-associated OPSCC, the high sensitivity and specificity of the established combination of p16 immunostain, DNA ISH, and HPV16 DNA amplification suggests that the introduction of labour- and cost-intensive mRNA ISH, is not necessary in the diagnostic routine of oropharyngeal tumors.