288 Low-Grade Sinonasal Tract Adenocarcinoma, of Non-Intestinal Type, Non-Salivary Type With S100 Expression

Abstract

Objectives: The World Health Organization classifies primary sinonasal adenocarcinomas (SNACs) into salivary and non-salivary types. Non-salivary SNACs are separated into intestinal-type (ITAC) and non-ITAC, with both having low-and high-grade categories. Low-grade non-ITAC is the most uncommon and hence one of the least-thought-of differential diagnoses. In contrast to ITAC, non-ITAC is a less aggressive adenocarcinoma with better clinical outcome. Therefore, its recognition and reliable separation from benign sinonasal glandular proliferations or more aggressive ITAC and salivary types are very important. Non-ITAC has been reported to share some features with seromucinous hamartomas including S100 expression. We herein report two cases of low-grade non-ITAC with S100 expression. Methods: Two cases of non-ITACs were included in the study. Clinical information, computed tomography (CT) imaging, and pathological results were analyzed. Hematoxylin and eosin (H&E), and S100, CK7, CK20, CDX2, TTF-1, napsin-A, synaptophysin, and chromogranin antibody staining were performed. Results: The two tumors occurred in elderly patients. CT scans demonstrated soft tissue masses in their nasal cavities. Histology showed subepithelial cellular neoplastic proliferations of monotonous bland round cells forming tightly packed and anastomosing tubules and trabeculae. High-power view showed low-grade cytological atypia with minimal pleomorphism and hyperchromasia. Small psammoma bodies were also seen. Both tumors had CK7+/CK20-immunophenotype. TTF-1, napsin-A, synaptophysin, and chromogranin stains were negative. Both tumors showed strong cytoplasmic and nuclear staining for S100. Conclusion: The finding of S100 staining in both cases is consistent with previously reported incidence of greater than 70%. S100 stain may increase diagnostic sensitivity and specificity, when combined with CK7 and CK20 to differentiate sinonasal non-ITAC from ITAC. On the other hand, distinguishing non-ITAC from salivary types such as adenoid cystic carcinoma, which also expresses S100, can be achieved by paying close attention to cytomorphology.