PROMOTIONAL EFFECTS OF AZATHIOPRINE ON PERIPHERAL B-CELL LYMPHOMAS INBALB C MICE INDUCED BY ADMINISTRATION OF 7,12-DIMETHYLBENZ[A]ANTHRACENE/

BALB/c mice either were injected subcutaneously with 25 mug/g or 50 mu g/g body weight 7,12-dimethylbenz[a]anthracene (DMBA) at the age of 13 weeks, or received repeated s.c. injections of azathioprine (0.1 mg/g ) starting from the age of 6 or 18 weeks, or they received treatments with both agents. Of the 317 mice treated, 69 developed lymphomas by t he age of 50 weeks. None of the 31 non-treated mice developed lymphoma s during this period. The lymphomas, classified according to Pattengal e-Taylor's classification for murine lymphomas/leukemias, were examine d immunohistochemically and immunogenetically. The lymphomas induced w ith DMBA showed a male preponderance and a higher incidence of the B c ell type, especially in the lymph node and spleen. Azathioprine induce d predominantly T-lymphoblastic lymphomas in the thymus and these were found more frequently in females. Treatment with both DMBA and azathi oprine remarkably increased the incidence of B lymphomas, especially f ollicular center cell lymphomas in the spleen, which are the predomina nt type of spontaneous lymphomas occurring in older BALB/c mice. Some of the treated mice also developed prelymphomatous lesions.