Lack of tumor-promoting ability of certain environmental chemicals in a two-stage mouse skin tumorigenesis assay

The food antioxidants butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA) were tested as tumor promoters on CDl female mice initiated with 7,12-dimethylbenz(a)anthracene (DMBA). At a dose of 1 mg twice weekly they did not promote skin tumors. Nor did they produce tumors when tested as a complete carcinogen without DMBA initiation. The polychlorinated biphenyl Aroclor 1254 (PCB) and the polybrominated biphenyl Firemaster-6 (PBB) were also tested for their ability to promote skin tumors; at a 100 μg dose twice weekly they were inactive. The environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) at a dose of 0.1 μg twice weekly did not promote skin tumors in DMBA-initiated mice. TCDD, PCB, and PBB did not promote spontaneous tumors. None of the compounds at the dosages tested significantly increased the intrafollicular epidermis, nor did they appear to be chronically toxic to the test animals. These results indicate that dosage may be an important factor in promotion, since several of the tested compounds are known to be promoters in pulmonary and hepatic systems.