A Durable Response in Sinonasal Undifferentiated Carcinoma Treated With Subtotal Resection and Ultra-Early Postoperative Chemoradiotherapy: A Case Report.

Sinonasal undifferentiated carcinoma (SNUC) is a rare and aggressive malignancy that arises in the nasal cavity and paranasal sinuses. Although gross total resection (GTR) is associated with improved local control and survival, the anatomical complexity and frequent skull base invasion often render complete resection infeasible. In such cases, the timing of postoperative therapy may be critical for disease control. We report a case of a 68-year-old man with stage IV SNUC who underwent subtotal endoscopic resection, followed by ultra-early postoperative concurrent chemoradiotherapy (CCRT) initiated within one week of surgery. CCRT was delivered using intensity-modulated radiation therapy (IMRT) and cisplatin (CDDP). The patient achieved a complete response with no evidence of recurrence at six-year follow-up. This case underscores the potential for durable disease control through timely multimodal therapy in anatomically unresectable cases where GTR is not feasible. While GTR remains the optimal goal when achievable, early postoperative chemoradiotherapy may offer meaningful benefit in selected patients with subtotal resection. We discuss the significance of treatment timing, surgical extent, and multidisciplinary planning in the context of recent literature.