Neuroendocrine tumors are rare and highly heterogeneous neoplasms with a wide spectrum of histological differentiation, functional, and biological features. Small cell neuroendocrine carcinomas (SNECs) of the sinonasal tract are particularly rare. Pathological features of SNECs of the nasal cavity and paranasal sinuses, which are aggressive tumors, are similar to those of anaplastic small cell carcinomas of the lung. We present a case of high-grade sinonasal SNECs in a patient with Xeroderma pigmentosum complementation group C (XPC) gene-positive xeroderma, which, to our knowledge, is the first case reported worldwide. Keywords: NET; XPC; nasal cavity; nasopharynx; neuroendocrine carcinoma; small cell carcinomas; xeroderma.

2024