Selective enhancement of radiation response in a C3H mammary carcinoma by cisplatin

The interaction between cisplatin and radiation was studied in a C3H mammary carcinoma and its surrounding normal skin. Treatment with 6 mg/kg of cisplatin given 30 mins before irradiation enhanced the radiation response in the tumor by a factor of 1.7, whereas the same drug treatment given immediately after or 4 hrs after irradiation only enhanced the effect by a factor of 1.2--1.3. No interaction between radiation and cisplatin was observed in the surrounding skin. It is hypothesized that in the C3H mammary carcinoma the prominent radiation-modifying effect of cisplatin given before radiation is due to a radiosensitization involving hypoxic tumor cells combined with a tumor cell-destructive effect of the drug itself.