Human Papillomavirus-Associated Combined Neuroendocrine and Squamous Cell Carcinoma of the Sinonasal Tract.

Combined neuroendocrine and squamous cell carcinoma (SCC) of the sinonasal tract is rare entity but is increasingly gaining recognition within the head and neck pathology community. In a recent series, a single case was reported to demonstrate diffuse p16 positivity despite lacking high-risk human papillomavirus (HPV) by RNA in-situ hybridisation (ISH). Here we describe a case of p16 positive combined neuroendocrine and SCC containing high-risk HPV. Retrospective case review of sinonasal carcinomas within the Head and Neck Pathology Department at Guy's and St Thomas' NHS Foundation Trust identified a single case of combined neuroendocrine and SCC. Clinico-demographic data was obtained through electronic hospital records. All immunohistochemistry and in-situ hybridisation were undertaken according to departmental standard operating procedures. Routine microscopy showed the tumour to comprise small and large cell neuroendocrine components as well as squamous and spindle cell elements. Small and large cells demonstrated CD56 and synaptophysin expression, whereas CK5/6 and p63 were confined to squamous components. There was diffuse p16 expression and punctate nuclear positivity for DNA ISH. We describe a case of HPV-associated combined neuroendocrine and SCC of the sinonasal tract. Recognition of HPV association with this entity avoids diagnostic pitfalls.