Chemotherapeutic implications of early tumor cell growth in an animal brain-tumor model.

The onset of tumor cell proliferation was determined in an animal brain-tumor model in which tumor cells had been injected into the cerebrum of rats through a hollow stainless steel screw implanted stereotactically. Tritiated thymidine uptake in the DNA at various periods after injection of tumor cells indicated no significant proliferation of tumor cells until 168-192 hours post implantation, after which tritium uptake increased exponentially. Control rats with screws alone or screws through which balanced salt solution had been injected showed an increased uptake at 72 hours, a phenomenon not observed in animals given tumor cells. Our findings suggested that, in the tumor model described, experimental chemotherapy tests should be deferred until at least 7 days post implantation.