Primary Maxillary Sinus Neuroendocrine Carcinoma: Insights from Immunohistochemical Diagnosis to Non-surgical Management and Literature Review

Abstract

Aims: Primary neuroendocrine carcinoma (NEC) of the maxillary sinus is extremely rare, and optimal management remains undefined. We report a case of poorly differentiated NEC of the maxillary sinus and review published literature to provide a comprehensive overview of diagnostic and therapeutic strategies. Presentation of Case: A 57-year-old man presented with a poorly differentiated NEC of the left maxillary sinus. Histopathology showed high-grade morphology with immunopositivity for synaptophysin, CD56, and EMA, and a Ki-67 index of ~80%, while p40 and S-100 were negative. The patient was treated with seven cycles of cisplatin-etoposide chemotherapy followed by 60 Gy external beam radiotherapy. Surgery was avoided, preserving the orbit. At three years of follow-up, he remains in complete clinical and radiological remission. Discussion: Diagnosis of sinonasal NEC relies on immunohistochemistry to distinguish it from other small round-cell malignancies. Literature review of reported primary sinonasal NECs, including maxillary cases, reveals heterogeneity in management, with most patients undergoing surgery combined with chemoradiotherapy. Our case demonstrates the potential role of definitive chemoradiotherapy as an organ-preserving approach in select patients with high-grade NEC. The collated data from existing reports highlight variability in outcomes, underscoring the need for standardized treatment protocols. Conclusion: This case illustrates long-term remission of maxillary sinus NEC achieved with non-surgical multimodality treatment. By consolidating available literature, our report provides a concise reference on sinonasal NECs and supports consideration of organ-preserving, response-adapted strategies in appropriately selected patients.