Cancer patients often have subclinical
vitamin A deficiencies and low
vitamin A lung levels. Previous studies showed that subclinical
vitamin A deficiency increased the severity of
pneumonitis induced by whole-lung irradiation in rats. Many studies have shown that lung irradiation increases the number of lung
tumors developing from intravenously injected
tumor cells in mice. We examined the impact of
vitamin A deficiency on the development of lung
metastases from a highly metastatic syngeneic rat
rhabdomyosarcoma in normal rats and rats receiving prior lung irradiation. Weanling female WAGrijY rats were randomized to receive either a diet lacking both
vitamin A and
beta-carotene or a control diet. After five weeks, the deficient diet significantly decreased levels of
retinol in the lung and liver but not in the serum, modeling the tissue and blood levels seen in prior studies of patients with subclinical
vitamin A inadequacy. The
vitamin A-deficient diet did not alter the number of lung
tumors developing from intravenously injected
tumor cells in unirradiated rats. Whole-lung irradiation produced dose-dependent increases in the number of lung
tumors developing from
tumor cells injected intravenously one or 29 d after irradiation.
Vitamin A deficiency did not alter these dose-response curves, indicating that the more intense radiation-induced
pneumonitis seen previously in
vitamin A-deficient rats did not alter the enhancement of
metastases produced by whole-lung irradiation. Moreover, inadequate
vitamin A intake did not influence the growth of
tumors implanted subcutaneously or increase the number or size of the spontaneous lung
metastases developing from these subcutaneous
tumors. Thus, although low
vitamin A status influences the development of
lung injury and is considered a possible modifiable risk factor increasing risk of primary
cancer, it did not affect the growth of subcutaneous
tumors or increase the development of artificial or spontaneous lung
metastases in this rat model.