True histiocytic lymphoma: an immunohistochemical and ultrastructural study of two cases.

Immunologic studies demonstrate that non-Hodgkin's lymphomas are derived predominantly from B- or T-lymphoid cells, while node-based tumors of true histiocytic derivation are rare, with few documented cases. This report describes the clinical, histologic, immunohistochemical, and ultrastructural features of two cases of node-based true histiocytic lymphoma. Distinctive ultrastructural features included numerous cytoplasmic lysosomes, surface microvillous processes, and occasional cell junctions, and the cells stained strongly for alpha-napthyl acetate esterase and alpha one-antitrypsin. Since there are few specific histologic features, special technics may be essential in confirming the diagnosis of true histiocytic lymphoma, and determining appropriate therapy.