Carcinogenic effects of infantile and long-term 2,3,7,8-tetrachlorodibenzo-p-dioxin treatment in the mouse.

An infantile carcinogenesis assay was carried out with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) injections administered intraperitoneally at 0, 1, 30 and 60 micrograms/kg b.w. doses to (C57BL/6J X C3Hf)F1 (B6C3) and to (C57BL/6J X BALB/c)F1 (B6C) mice, starting from the 10th day of life, once weekly repeated 5 times. Animals were then observed until 78 weeks of age. The induction of thymic lymphomas was related to treatment at 60 micrograms/kg dose level in both sexes of both hybrids, and at 30 micrograms/kg dose level in both sexes of B6C mice and in male but not female B6C3 mice. The incidence of hepatocellular adenomas was increased by TCDD treatment at 60 micrograms/kg dose level in B6C3 of both sexes but not in B6C mice. Hepatocellular carcinomas were seen at increased incidence at 30 and 60 micrograms/kg doses in B6C3 males but not in B6C3 females or in B6C mice of both sexes. The incidence of other tumor types was not related to treatment in both hybrids. A long-term carcinogenesis bioassay with TCDD was carried out in B6C3 mice treated by gavage at 0, 2.5 and 5.0 micrograms/kg b.w. doses from 6 weeks of age, once weekly for 52 weeks. The animals were observed until 110 weeks of age. An increased incidence of hepatocellular adenomas and carcinomas was related to treatment, at both doses and in both sexes. The incidence of other tumor types was uniformly low in treated and control groups, without any association with treatment, in both sexes.