Induction of thyroid tumors in (C57BL/6N x C3H/N)F1 mice by oral administration of 9-3',4',5',6'-tetrachloro-o-carboxy phenyl-6-hydroxy-2,4,5,7-tetraiodo-3-isoxanthone sodium (Food Red 105, rose bengal B).

The tumorigenicity of 9-3',4',5',6'-tetrachloro-o-carboxy phenyl-6-hydroxy-2,4,5,7-tetraiodo-3-isoxanthone sodium (CAS: 632-68-8) [also called Food Red 105 (FR 105) or Rose Bengal B], which is widely used for food or cosmetic coloring in Japan, was examined in (C57BL/6N X C3H/N)F1 mice. Animals were divided into 6 groups with 50 mice in each group, and they were given solutions of 0, 0.125, and 0.5% FR 105 in the drinking water starting at 6 weeks of age and ending at 101 weeks. The mean relative thyroid weights in both sexes of mice given 0.125 and 0.5% FR 105 were significantly increased compared to those of controls. Enlarged thyroid glands were composed exclusively of colloid goiters characterized by distended follicles lined with flattened follicular cells. The male mice given 0.5% FR 105 had follicular adenomas in the thyroid gland at an incidence of 22.9%, which was significantly higher than the incidence in controls (P less than .005). Radioactive 131I uptake in colloid goiters was markedly decreased compared to that in intact thyroid glands. The results indicate that FR 105 can induce colloid goiters and thyroid adenomas in a dose-dependent manner.