High-risk follicular dendritic cell sarcoma of the tonsil mimicking nasopharyngeal carcinoma.

Follicular dendritic cell sarcoma (FDCS) is often misdiagnosed as a carcinoma or malignant lymphoma due to morphological variability. In FDCS application of routine antibody panels without CD21 and CD23 increases the misdiagnosis rate, because the tumor cells often show focal positivity for usual immunohistochemical markers. Our new case showed a distinct picture due to the uncommon tumor architecture, with extensive areas of necrosis and hemorrhage, the presence of nuclear atypia, and an increased mitotic count and Ki-67 index. These features suggest the classification of this tumor in the category of high-risk malignancies, with uncommon features of FDCSs.