Chemoprevention of tumor development and metastasis of transplantable hepatocellular carcinomas in rats by vitamin A.

Vitamin A is attracting increasing attention as a potential cancer chemopreventative agent. To investigate the effect of vitamin A on tumor establishment, growth and metastasis, rats were fed diets containing zero, adequate or excess (100X adequate) amounts of vitamin A prior to subcutaneous injection with transplantable hepatocellular carcinomas derived from solid tumors induced by N-2-fluorenylacetamide. When rats were injected at the same time the dietary regimen was begun, tumor growth was similar in both the deficient and adequate vitamin A groups with 20% less in the excess vitamin A group. However, when rats were injected 2 weeks post-initiation of the dietary regimen, tumors were fewer and appeared later under conditions of either vitamin A deficiency or excess. When rats were injected with a metastatic line 2 weeks following initiation of the dietary regimen, no metastases were observed in the animals fed excess vitamin A, but 60% had metastases in the deficient group and 75% in the adequate group. Results suggest that dietary extremes of vitamin A affect tumor establishment and growth and excess amounts prevent metastasis of transplantable hepatomas in the rat.