The roles of vitamin A in the prevention of neoplastic diseases: a critical assessment.

The role of vitamin A and its analogs (retinoids) in the prevention and therapy of neoplastic diseases is discussed. Epidemiological data showing a relationship between vitamin A deficiency and increased frequency of tumors in man and animals are examined and the experimental models demonstrating the protective action of retinoids in the respect of both spontaneous and induced neoplasias of animals are reviewed. Among the possible mechanisms responsible of the antineoplastic activity, the immunopotentiating effect is underlined. Some toxicological aspects of retinoids administration and the consequent application of the experimental results in human medicine are finally discussed.