[Follicular dendritic cell sarcoma: an unusual tumor with nodal and extranodal presentation. Clinicopathological and immunohistochemical study of five cases].

Dendritic cells (DC) are an essential component of the nonlymphoid, nonphagocytic immunoaccessory reticulum cells of the peripheral lymphoid tissue. Follicular dendritic cells (FDC) are one type of DC in the lymphoid follicle associated with B lymphocytes. They play an important role in the uptake and presentation of antigen generation and regulation of immune complexes. FDC can be recognized histologically by their oval to triangular nucleus, delicate basophilic nuclear membrane, almost empty nucleoplasm, small but distinct central nucleolus, and indistinct cellular outline; some cells can be binucleated or multinucleated. Ultrastructurally, they possess delicate interwoven cell processes connected by desmosomes. Immunohistochemically, they can be highlighted by staining with CD21, CD35, R4/23, Ki-M4, CNA.42 and CD68 (Kp-1) (l-4). FDC sarcoma is rare. FDC sarcomas affected predominantly lymph nodes with occasional extranodal involvement. Many cases of FDC sarcomas are probably misdiagnosed as other tumors such as large cell lymphoma, sarcomatoid carcinomas, fusocellular sarcomas or melanomas. We present five cases of FDC sarcomas and discuss the salient clinical, pathological and immunohistochemical features of these tumors.