Intra-abdominal follicular dendritic cell sarcoma with marked pleomorphic features and aberrant expression of neuroendocrine markers: report of a case with immunohistochemical analysis.

Follicular dendritic cell sarcoma (FDCS) is a very rare malignant tumor arising most frequently in lymph nodes with only few reports of extranodal locations. We report the case of a 35-year-old man with a large retroperitoneal mass. Histologically the tumor was composed of highly pleomorphic cells exhibiting some uncommon features such as an epithelioid appearance, cystic spaces, and multinucleated cells with morphologic features of emperipolesis.