Experimental studies on the radiation-modifying effect of bleomycin in malignant and normal mouse tissue in vivo.

The interaction between bleomycin (BLM) and radiation was studied in a C3H mammary carcinoma and its surrounding normal skin. In the skin, single and fractionated doses of sequential treatment with BLM (25 mg/kg) 24 hours prior to radiation therapy did not influence the response to irradiation, whereas simultaneous treatment with BLM given 15 minutes before radiation therapy enhanced the reaction to irradiation by a factor of 1.2 or 1.4 following treatment with one fraction or five fractions, respectively. The tumor response to irradiation was not influenced by a single sequential treatment, but five daily fractions of radiation therapy following five daily dose fractions of BLM increased the radiation dose needed to control 50% of the tumors, probably because the tumors continued to grow during the BLM treatment. Simultaneous treatment enhanced the response to irradiation by a factor of 1.2 after both single-dose and fractionated therapy. Based on these data it was concluded that none of the combined treatment schedules were able to produce a better therapeutic effect than radiation therapy alone. Furthermore, mortality due to lung fibrosis in mice treated with BLM indicated the marked toxicity of the drug. This toxicity was most pronounced after fractionated treatment and when radiation therapy and BLM were given simultaneously.