Pleomorphic reticulum cell sarcoma, monoclonal gammopathy and amyloidosis: an immunoperoxidase study.

Pleomorphic reticulum cell sarcoma, a histologic variant of the histiocytic lymphomas, presented as an abdominal mass in a 52-year-old woman. Extensive amyloid deposition was present within the tumor mass and an M-component (IgG Lambda) was identified in the serum. Direct immunoperoxidase staining of tissue sections demonstrated the same monoclonal immunoglobulin to be present within the neoplastic cells, presumptive evidence of their ability to both synthesize and secrete immunoglobulin. The presence of amyloid within this patient was probably the direct result of the tissue deposition of this monoclonal immunoglobulin and may be related to the amyloidogenic nature of Lambda light chains. Immunoglobulin production is a specific property of the B lymphocyte series. Transforming B lymphocytes and their differentiating progeny are engaged in active immunoglobulin synthesis and thus may be distinguished from morphologically identical but functionally distinct cells. The demonstration of cytoplasmic monoclonal immunoglobulin within these "malignant reticulum cells" strongly supports the assertion that at least some "histiocytic lymphomas" are neoplastic analogues of transformed B lymphocytes, and are not derived from phagocytic histiocytes, as previously believed.