Squamous and Neuroendocrine Specific Immunohistochemical Markers in Head and Neck Squamous Cell Carcinoma: A Tissue...

The performance characteristics of neuroendocrine-specific and squamous-specific immunohistochemical markers in head and neck squamous cell carcinomas (SCC), in particular in oropharyngeal tumors in this era of human papillomavirus (HPV)-induced cases, are not well-established. The differential diagnosis for poorly differentiated SCCs, for nonkeratinizing oropharyngeal SCCs, and for other specific SCC variants such as basaloid SCC and undifferentiated (or lymphoepithelial-like) carcinomas includes neuroendocrine carcinomas. Given that neuroendocrine carcinomas of the head and neck are aggressive regardless of HPV status, separating them from SCC is critically important. In this study, we examined the neuroendocrine markers CD56, synaptophysin, and chromogranin-A along with the squamous markers p40 and cytokeratin 5/6 in a large tissue microarray cohort of oral, oropharyngeal, laryngeal, and hypopharyngeal SCCs with known HPV results by RNA in situ hybridization for the oropharyngeal tumors. Results were stratified by site and specific SCC variant. The neuroendocrine stains were rarely expressed in SCC (<1% overall) with CD56 the least, and chromogranin-A the most, specific markers. Further, p40 and cytokeratin 5/6 were very consistently expressed in all head and neck SCC (>98% overall), including very strong, consistent staining in oropharyngeal HPV-related nonkeratinizing SCC. Undifferentiated (or lymphoepithelial-like) carcinomas of the oropharynx are more frequently p40 or cytokeratin 5/6 negative or show only weak or focal expression. In summary, markers of neuroendocrine and squamous differentiation show very high specificity and sensitivity, respectively, across the different types of head and neck SCC.