The oncogenic effect of immunosuppressive (cytotoxic) agents in (NZB x NZW) mice. II. Emergence of tumors in young animals treated with azathioprine and ifosfamide, including a histologic assessment of the neoplasms.

The age of (NZB x NZW) mice treated with immunosuppressive agents has been associated with an increased incidence of neoplastic disease in certain experimental situations. In this study, azathioprine administered daily over a period of 7 to 8 months significantly increased the occurrence of malignancies in animals aged 6 to 12 weeks at the start of treatment. No such increase was observed for ifosfamide. The resulting lesions observed in azathioprine and ifosfamide treated hybrids were predominantly lymphomas (60 to 80%) and could be classified according to two histologic types: Type I and II. The lymphomas in the ifosfamide groups could not be distinguished histologically from those in the azathioprine groups.