Follicular dendritic cell sarcoma with immature T-cell proliferation.

Follicular dendritic cell sarcoma is characterized by proliferation of spindled to ovoid cells reminiscent of follicular dendritic cells. However, the association of follicular dendritic cell sarcoma with a dense infiltration of immature T cells has not hitherto been reported. We report an unusual case of follicular dendritic cell sarcoma of the mesentery with immature T-cell proliferation in a 68-year-old man. The infiltrating immature T cells demonstrated expression of CD3, CD1a, TdT, and coexpression of CD4 and CD8 by immunohistochemistry. In addition, the patient was subsequently diagnosed with myasthenia gravis and paraneoplastic pemphigus and died of distant metastasis within 2 years after initial diagnosis of follicular dendritic cell sarcoma. The aggressive clinical course of this case contrasts with the indolent course of follicular dendritic cell sarcomas, and thus, the prognostic implications of follicular dendritic cell sarcoma with immature T-cell proliferation require clarification. The complication of myasthenia gravis and paraneoplastic pemphigus may suggest that immature T-cell proliferation has an autoimmunity-related systemic influence.