Follicular dendritic cell sarcoma mimicking diffuse large cell lymphoma: a case report.

Follicular dendritic cell sarcomas (FDCSs) are rare tumors arising from follicular dendritic cells in lymphoid tissue. Fewer than 20 cases have been described in the English-language literature. We describe the second case of an FDCS with primary liver involvement. The initial diagnosis was lymphoma, and appropriate treatment was prescribed. After the initial treatment failed, additional biopsy samples were obtained. Standard pathologic analysis and immunophenotyping for a panel of monoclonal antibodies were performed on formalin-fixed paraffin-embedded tissue and frozen sections. The pathologic findings were consistent with FDCS, and the specimens showed some of the characteristic pathologic features suggestive of this tumor, including multinucleation and a spindle pleomorphic morphology. The tumor cells were positive for S-100 protein, CD45, CD14, and vimentin. Because of its morphological characteristics, FDCS can be confused with other neoplastic entities, such as lymphomas and other solid tumors.