Follicular dendritic cell sarcoma of the tonsil: A rare entity

Follicular dendritic cells (FDC) are nonlymphoid, nonphagocytic accessory cells in the immune system. They have major roles in antigen presentation and regulation of germinal center reaction. FDC sarcoma is a rare and under-recognized malignancy. Most of the cases are reported in the lymph nodes. The typical morphology is syncytial aggregates of oval/spindly cells with vesicular bland nuclei and small nucleoli. Focal whorling and storiform pattern, multinucleate giant cells, and the presence of small lymphocytes in the background give additional clues for the diagnosis. As spindle cell tumors are rare in the lymph nodes, FDC sarcoma comes under the differential diagnosis of spindle cell neoplasms of the node and an accurate diagnosis is often rendered. However, when the neoplasm occurs in extranodal sites, the diagnosis is often missed because the FDC markers are not routinely used in the immunopanel for undifferentiated neoplasms. Because of its rarity, the extranodal FDC sarcomas pose a great diagnostic challenge and often misdiagnosed initially. Herein, we report a case of FDC sarcoma of the tonsil in a 36-year-old female patient. Biopsy of the lesion showed oval to spindly cells in syncytial sheets and focally in whorled pattern. The individual cells were having plump vesicular nuclei and small nucleoli. Occasional multinucleate cells and sprinkling of lymphocytes within the tumor were also noted. The tumor cells were positive for CD23 and CD35. A diagnosis of FDC sarcoma was given. Greater awareness of the morphologic spectrum of FDC sarcoma and appropriate immunostains for FDC differentiation will help in recognition of this rare neoplasm.