Inhibition of growth of Shope rabbit papilloma by hypervitaminosis A.

Abstract

Vitamin A retards the growth and delays the initial appearance of the Shope rabbit papilloma when administered systemically in high dosage. Such treatment, when continued long enough, causes atrophy of the fleshy portion of the papilloma. In some rabbits this may be followed by shedding of the keratinized portion of the papilloma and macroscopic disappearance of the tumor. When treatment is stopped, such tumors regrow. Microscopic examination of the tumors suggests that these effects are brought about either by acceleration of differentiation and keratinization of the epithelial papilloma cells or by inhibition of their mitotic rate. Observations were made suggesting that excess vitamin A may cause a moderate increase in concentration of infective virus in papillomas grown on wild rabbits. It is thought that this effect could be due to the higher proportion of keratinized material in vitamin A-treated papillomas.