INDUCTION OF THYMIC LYMPHOMA IN MICE ADMINISTERED THE DIDEOXYNUCLEOSIDE DDC

Groups of 10 male and 20 female B6C3F1 mice received 0, 500, or 1000 m g/kg/day 2',3'-dideoxycytidine (ddC) by gavage for 13 weeks. At the en d of the 13-week exposure period all males and 10 females per group we re necropsied while the remaining females were held for 1 month withou t further treatment. Thymic atrophy was present at the 13-week necrops y in male and female mice administered 1000 mg/kg/day and in females a dministered 500 mg/kg/day, but was not present in females following 1 month of recovery. Thymic lymphoma was present in 1 female that receiv ed 500 mg/kg/day and 1 female that received 1000 mg/kg/day. In a follo w-up study groups of 70 female mice received 0, 500, or 1000 mg/kg/day for 13 weeks. At the end of the 13-week exposure period 20 mice per g roup were necropsied and the remaining animals held for 3 months witho ut further treatment. Thymic atrophy was observed in ddC-exposed group s at the 13-week necropsy but not in mice allowed to recover for 13 we eks. Thymic lymphoma occurred in 3/50 mice that received 500 mg/kg/day and in 17/50 mice that received 1000 mg/kg/day but did not occur in m ice from the vehicle control group. (C) 1995 Society of Toxicology