Enhancement of the induction of murine thymic lymphomas by cyclosporine.

The effects of cyclosporine (CsA) on the induction of thymic lymphoma in male Swiss Webster mice were investigated using the classic model of two-stage carcinogenesis with N-methyl N-nitrosourea (MNU) as an initiator and CsA as a promoter. The mice treated with a single dose of MNU followed by chronic feeding of 0.015% CsA developed an eight-fold higher incidence of thymic lymphomas than the mice treated with a single dose of MNU followed by a basal diet. No mice treated with CsA alone or mice kept on a basal diet developed tumors. The results suggest that CsA enhances the induction of thymic lymphomas by its promoting effect and that the disturbance of thymic microenvironment induced by CsA may be one of the underlying mechanisms of the promoting action by CsA.