Growth kinetics of mammary tumor 13762 in rats previously cured by chemotherapy.

We studied the growth capabilities of mammary tumor 13762 transplanted into inbred F344 rats previously cured of tumors by cell kinetically based sequential chemotherapy. Of the 18 challenge tumors, 4 were completely rejected, and nonrejected tumors grew at subnormal rates. The subnormal growth was specific for the cured rats because tumor growth in age- and therapy-matched non-tumor-bearing controls was normal. Cell kinetic studies with the use of in vitro techniques for the [3H]dThd labeling index, DNA synthesis time, and primer-dependent DNA polymerase labeling index (an in vitro estimate of growth fraction) indicated that the subnormal growth rates of the 13762 tumor in cured rats were due to subnormal tumor cell production. Cell loss rates were similar in tumors growing in cured rats and in size-matched tumors growing in normal controls. The results are consistent with the possibility that the subnormal growth of 13762 challenge tumors in chemotherapeutically cured F344 rats was mediated by immune factors.