Antitumor activity of beta-carotene, canthaxanthin and phytoene.

Mice were given either beta-carotene or either of two carotenoids with no vitamin A activity--canthaxanthin or phytoene--or placebo. Skin tumors were induced in each group by each of three methods: (1) UV-B (290--320 nm); (2) dimethylbenz(a)anthracene (DMBA)/croton oil applications; (3) DMBA followed by low-dose UV-B. For tumors induced by UV-B alone, beta-carotene-phytoene- and canthaxanthin-treated mice developed fewer tumors per mouse, with a delay in tumor appearance, than did control mice. For tumors induced by DMBA/croton oil or DMBA/UV-B, mice receiving beta-carotene showed a significant difference in tumor numbers and appearance time from placebo mice; phytoene and canthaxanthin treatment had no effect.