Microsatellite instability and proliferating activity in sinonasal carcinoma: molecular genetic and immunohistochemical comparison with oral squamous cell carcinoma.

Sinonasal carcinomas arise from the respiratory epithelium that lines the nasal and paranasal cavities, and are histologically composed of either squamous or cylindrical cell carcinoma. However, molecular analysis with the purpose of distinguishing sinonasal carcinomas from other head and neck squamous cell carcinomas (HNSCCs), which arise from squamous epithelium, has been limited. Moreover, a wide range of frequency of microsatellite instability (MSI) in HNSCC has been reported. Using high-resolution fluorescent microsatellite analysis (HFRMA), we studied microsatellite alterations in 34 patients with sinonasal carcinoma. As a control, 24 oral squamous cell carcinomas were used. MSI was detected in 14 patients with sinonasal carcinoma (41%), but not in any with oral squamous cell carcinoma (p=0.002). Furthermore, in sinonasal carcinoma, 11 out of 17 (65%) T1-T3 sinonasal carcinomas demonstrated MSI, whereas only 3 out of 15 (20%) T4 tumors demonstrated MSI. Immunohistochemically, sinonasal carcinoma showed a higher MIB-1-labeling index and more frequently showed cytokeratin 18 expression when compared with oral squamous cell carcinoma. These findings suggest that sinonasal carcinoma and HNSCC have quite different molecular backgrounds regarding carcinogenesis, and the role of MSI is relatively minor in cases of advanced sinonasal carcinoma.