Accelerated growth of mammary tumor cells in normal and athymic mice after treatment in vitro with dexamethasone.

The tumorigenicity of dexamethasone-treated tissue-cultured mammary tumor cells was compared to that of untreated mammary tumor cells. The dexamethasone-induced cells progressed faster in normal syngeneic animals than did untreated mammary tumor cells. The fact that the growth rate differential was also observed in athymic mice suggests that T-lymphocyte-mediated immunity was not a factor in the accelerated progression in vivo of the tumor cells that had been cultured in the presence of dexamethasone.