Carcinogenesis studies of eugenol (>99% pure), a widely used flavor additive and chemical intermediate, were conducted by feeding diets containing 6,000 or 12,500 ppm of eugenol to groups of 50 female F344/N rats and by feeding diets containing 3,000 or 6,000 ppm to groups of 50 male F344/N rats and B6C3F1 mice of each sex for 103 weeks. Groups of 40 rats and 50 mice of each sex served as controls. Dose levels selected for the two year studies were based on thirteen-week (91-day) studies in which dietary concentrations for the six groups ranged from 0 to 12,500 ppm. Other than a -10% difference from controls in body weights in the 12,500 ppm male rats, no chemically related gross or histopathologic effects were observed.
In the two-year studies, with the exception of the high dose female rats and female mice, final body weights of the treated groups were comparable to their respective controls. No significant differences in survival were apparent for any of the eight groups receiving eugenol and for the appropriate controls. Food consumption among groups was not different in comparison with controls-- rats: males equal to or greater than 97%, females equal to or greater than 91%; mice: males equal to or greater than 94%, females equal to or greater than 90%.
There were no significant observable differences between treated and control groups of rats for either nonneoplastic (toxic) lesions or neoplasms that could be attributed to eugenol. Increases in tumor incidences were diagnosed for low dose male rats with alveolar, bronchiolar adenomas or carcinomas (combined), for C-cell adenomas of the thyroid gland in low dose female rats, and for endometrial stromal polyps of the uterus in high dose female rats. Fibroadenomas of the mammary gland were decreased in dosed groups of female rats compared with controls. None of these differences were considered to be associated with the dietary administration of eugenol.
In male mice, the low dose animals had an increased incidence (P<0.05) of both hepatocellular adenomas (control, 4/50; low dose, 13/50; high dose, 10/49) and hepatocellular carcinomas (10/50, 20/50, 9/49) when compared with control animals. A significant increase in hepatic neoplasms was not observed in high dose animals. No single liver tumor type was observed in female mice with a statistically significant increased incidence. When the incidences of female mice with hepatocellular adenoma or carcinoma were combined (2/50, 7/49, 9/49), there was a dose-related positive trend and the incidence of liver neoplasms in high dose animals was higher than in controls (P<0.05).
Eugenol was given in the diets of female F344/N rats (0, 0.6, or 1.25%) and of male F344/N rats and male and female B6C3F1 mice (0, 0.3, or 0.6%) for 103 weeks. Under these experimental conditions, there was no evidence of carcinogenicity observed for male or female rats. For mice there was equivocal evidence of carcinogenicity since eugenol caused increased incidences of both carcinomas and adenomas of the liver in male mice at the 3,000 ppm dietary level and because eugenol was associated with an increase in the combined incidences of hepatocellular carcinomas or adenomas in female mice.