Stimulation by neonatal treatment with vitamin A of spontaneous mammary tumor development in GRS/A mice.

Daily subcutaneous injections of 100 micrograms (290.4 IU) vitamin A for the first 5 days of postnatal life to highly inbred GRS/A female mice resulted in a substantial increase in the incidence of both pregnancy-dependent and autonomous mammary tumors. The incidences of pregnancy-dependent mammary tumors in the experimental and control mice were 35.7% and 8.7% (p less than 0.05) in the first litter and 89.3% and 65.2% in the second litter, respectively, whereas neonatal treatments had no effects on reproduction. The incidence of autonomous mammary tumors was significantly higher in the experimental mice than in the control after 9 months of age. All experimental mice developed autonomous mammary tumors by 13 months of age, at which time the incidence in the control group was 57.9%. A significant stimulation by neonatal vitamin A treatment of murine mammary tumorigenesis has not heretofore been reported.