Sinonasal Small Cell Carcinoma-Case Series of a Rare Malignancy.

Sinonasal small cell neuroendocrine carcinoma (SNEC) is an extremely rare and aggressive neoplasm that can arise in the sinonasal region. These tumors are associated with high morbidity and mortality, are difficult to diagnose, and are hard to treat. We describe 2 cases of this poorly understood malignancy and review imaging, pathology, and treatment decisions. A 41-year-old male and a 64-year-old female presented to a tertiary center in 2019 after developing nasal obstruction and were found to have sinonasal masses on imaging. Both biopsies showed strong expression of pancytokeratin with dot-like reactivity and expression of neuroendocrine markers chromogranin and synaptophysin. The findings were diagnostic of SNEC. Staging positron emission tomography/computed tomography and brain MRI were performed, and patients were discussed at a multidisciplinary tumor board. Neither had distant metastatic disease at presentation. One patient had no intracranial or orbital disease and underwent a subtotal endoscopic resection with adjuvant chemoradiation. The other patient demonstrated middle cranial fossa, dural, and orbital involvement as well as cranial nerve V palsy. This patient was treated with induction chemotherapy, followed by concurrent chemoradiation. Both patients are presently alive at 4 months follow-up, but one with persistent local disease and the other distant metastasis. Sinonasal small cell neuroendocrine carcinoma is a rare and poorly understood malignancy with an aggressive clinical course. Continued careful review of pathology and study of molecular features are needed for improved understanding of SNEC, and particularly for head and neck SNEC, to establish a staging system and better formulate treatment protocols.