An unusual case of follicular dendritic cell sarcoma of the omentum with pleomorphous morphology and aberrant cytokeratin expression

Abstract

Follicular dendritic cell sarcoma (FDCS) is an uncommon tumor arising from follicular dendritic cells (FDCs) in the lymph nodes or in extranodal sites. We herein report an unusual case of a 30-year-old man who presented with a FDCS of the omentum and massive liver involvement. The tumor proliferation was a diffuse growth composed by large and highly pleomorphic cells. On immunostaining, B and T cell markers; CD30, myeloid, and histiocytic markers; and S100 were negative whereas CD21, CD23, CD35, clusterin, and fascin were positive. Unexpectedly, large spectrum cytokeratin clone AE1/AE3 was focally and variably expressed. Despite the latter atypical finding and the misleading morphology, immunohistochemistry allowed for a conclusive diagnosis of FDCS.