Experimental cancer of the lung.Inhibition by vitamin A of the induction of tracheobronchial squamous metaplasia and squamous cell tumors

Syrian golden hamsters of both sexes received 10 intratracheal instillations each of 3 mg benzo[a]pyrene (BP) and 3 mg hematite suspended in 0.2 ml saline. One group received no further treatment and developed 13 squamous tumors and 13 cases of squamous metaplasia in 53 animals at risk. The second group, one week after the end of the BP treatment, started to receive twice weekly stomach tube feedings of vitamin A palmitate (5 mg or 5000 IU in 0.1 ml corn oil) continued for life. In this group of 46 animals at risk only one developed a microscopic squamous tumor in a bronchus and one developed a patch of squamous metaplasia in the trachea. The incidence of forestomach papillomas was also reduced markedly by vitamin A treatment. The authors suggest that vitamin A has a systemic inhibitory effect on the induction of squamous changes (metaplasia as well as benign and malignant squamous tumors) in the columnar mucous epithelium of the respiratory tract.