Post-transplant malignant lymphoma. Distinctive morphologic features related to its pathogenesis.

Malignant lymphoma developed in two patients after renal transplantation. In both, the central nervous system was involved. Histologic study of the tumors showed that they were composed of a monomorphous proliferation of cells characterized by a large vesicular nucleus, prominent basophilic nucleolus and strongly pyroninophilic cytoplasm. The tumors thus would be classified as "diffuse large lymphoid lymphomas with pyroninophilia" or "immunoblastic sarcomas" as described in the literature. Tumor cells resembled cells observed in the paracortex of antigenically stimulated lymph nodes, cells from malignant lymphomas in mice that were antigenically stimulated and from malignant lymphomas in patients with immunodeficiency diseases or autoimmune disorders. The distinctive morphologic features of the tumors in the transplant recipients described provide further evidence that long-term antigenic stimulation may be important in their pathogenesis.