Sinonasal undifferentiated carcinoma: report of two cases and review of the literature.

Sinonasal undifferentiated carcinoma is a rare, highly aggressive neoplasm of the paranasal sinuses. Approximately 40 cases of this neoplasm have been reported to date. Microscopically, this neoplasm is composed of medium-sized cohesive cells arranged in nests, ribbons, and trabeculae having hyperchromatic nuclei, often with prominent nucleoli. A high mitotic rate, tumor necrosis, and prominent vascular invasion are conspicuous features. Squamous or glandular differentiation is not observed at the light-microscopic level. It appears to be a unique, distinctive clinicopathologic process that must be distinguished microscopically from other, less aggressive "round cell" sinonasal neoplasms. In this article, two additional cases of this neoplastic process are reviewed. Aggressive, multimodal treatment may offer the best chance for local control, palliation, and, ultimately, survival of the patient. The optimal treatment of SNUC, however, has yet to be determined.