Successful Management of Advanced Sinonasal Undifferentiated Carcinoma Using Concurrent Chemoradiotherapy With Simultaneous Integrated Boost and Intensity-Modulated Radiation Therapy: A Case Report.

Sinonasal undifferentiated carcinoma (SNUC) is a rare and aggressive malignancy with a poor prognosis, often presenting at an advanced stage owing to nonspecific symptoms and delayed diagnosis. Although the understanding of the histological and immunohistochemical characteristics of SNUC has improved, treatment options remain limited, and patient outcomes are suboptimal. We present a case of advanced SNUC originating in the left nasal cavity of a 53-year-old man, with visual-field impairment as the primary symptom. Based on imaging and histopathological findings, including a high Ki-67 index, as well as immunohistochemical positivity for cytokeratin and CD56, the patient was diagnosed with Stage IVB SNUC. Given the extent of local invasion, surgical resection was infeasible, and concurrent chemoradiotherapy (CCRT) was selected as the primary treatment. The regimen consisted of platinum-based chemotherapeutic agents, including cisplatin and etoposide (PE), combined with intensity-modulated radiation therapy using the simultaneous integrated boost technique to optimize tumor targeting while sparing critical structures such as the optic nerve. Complete tumor resolution was confirmed by post-treatment magnetic resonance imaging, with no evidence of recurrence or metastasis at the three-year follow-up. The patient reported significant improvement in vision, including the resolution of left hemianopia, which contributed to an enhanced quality of life. This case highlights the efficacy of CCRT in achieving durable disease control and functional recovery in patients with advanced SNUC. These findings underscore the potential of precision radiotherapy techniques and multimodal strategies for managing this challenging malignancy.