Inhibition or enhancement of rat mammary tumors dependent on dose BCG

The effect of BCG on the growth of transplantable rat mammary tumors in W/Fu rats was studied. Admixture of mycobacteria to tumor cells in vitro prior to their injection in vivo either had no effect on or resulted in inhibition of or enhancement of the growth of the tumor transplants. Inhibition occurred at high and enhancement at low mycobacteria:tumor cell ratios. However, following suppression of local tumor growth with high doses of BCG, the growth of a second tumor graft was enhanced. Pretreatment of rats with BCG alone also enhanced the growth of a subsequent tumor graft. These results suggest an inverse relationship between the optimal dose of BCG for suppression of local tumor and that required to induced systemic immunity.