Histopathological and immunohistochemical clues to the illusive diagnosis of follicular dendritic cell sarcoma: A clinicopathological masquerader

Follicular dendritic cell sarcoma is a rare histiocytic and dendritic neoplasm mainly involving the lymph nodes and selective extranodal sites. They are often misdiagnosed due to nonspecific clinical, radiological, and morphological findings in addition to their rarity. Four cases described below had variable age of presentation, site of involvement, size of the lesion, and histopathological features. Application of an extensive immunohistochemical panel, including a combination of >1 dendritic cell marker, clinched the diagnosis. A combination of D2-40 and Cluster of differentiation 21 (CD21) worked best in establishing a definite role in the current series. Programmed death-ligand 1 (PD-L1) analysis was positive in two of the three cases where it could be performed. However, none of our cases had received immunotherapy. Prompt recognition of the described histopathology features and incorporation of novel immunohistochemical markers can translate to timely initiation of therapy for this aggressive disease.