Proceedings of the 2023 North American Society of Head and Neck Pathology Companion Meeting, New Orleans, LA, March 12, 2023: Navigating New Developments in High Grade Sinonasal Neuroendocrine and Neuroectodermal Neoplasms

Although the definitions of sinonasal neuroendocrine and neuroectodermal neoplasms did not change substantially in the 5th edition WHO Classification of Head and Neck Tumours, the diagnosis of olfactory neuroblastoma (ONB), small cell neuroendocrine carcinoma, and large cell neuroendocrine carcinoma remains quite challenging in practice. Ambiguities surrounding the amount of keratin expression allowable in ONB and the amount of neuroendocrine differentiation seen in sinonasal undifferentiated carcinoma (SNUC) lead to significant diagnostic discrepancies at the high grade end of this tumor spectrum. Furthermore, a group of problematic neuroepithelial tumors that show overlapping features of ONB and neuroendocrine carcinoma have never been recognized in formal classification schemes. Since publication of the 5th edition WHO, two new tumor entities have been proposed that help resolve these problems. Olfactory carcinoma is defined by high grade keratin-positive neuroectodermal cells with frequent intermixed glands and shows recurrent Wnt pathway, ARID1A, and RUNX1 alterations. IDH2-mutant sinonasal carcinoma is a molecularly-defined category that encompasses tumors with undifferentiated (SNUC), large cell neuroendocrine, and neuroepithelial phenotypes. This review will provide a practical overview of these emerging entities and their application to diagnostic challenges in the post-WHO sinonasal neuroendocrine and neuroectodermal tumor classification.

Olfactory Neuroblastoma and Olfactory Carcinoma: A Practical Review

In the sinonasal tract, two tumor types are defined by neuroectodermal differentiation. Olfactory neuroblastoma (ONB), the traditional member of this category, is a keratin-negative neuroectodermal neoplasm that has lobulated architecture and variable neurofibrillary matrix. Olfactory carcinoma (OC), a newly-recognized diagnosis in the sinonasal tract, has keratin-positive neuroectodermal elements frequently intermixed with well-formed glands. These two neuroectodermal entities can show substantial overlap with other sinonasal small round blue cell tumors that express neuroendocrine markers. This review provides a practical overview of the key clinical and diagnostic features of ONB and OC and their differential diagnosis.