Combined treatment of rat rhabdomyosarcoma R1H with mitomycin C and X-rays

The effects of mitomycin C (MTC) alone and in combination with radiation on R1H rhabdomyosarcomas in WAG/Rij rats were studied. Growth delay was determined from tumor volume growth curves and proportion of tumor and host cells from flow cytometry measurements. Only minor growth delays were obtained with MTC at doses near the toxic level while irradiation applied in three fractions of 10 Gy in three weeks yielded growth delays of 27, 44, and 51 days measured at volumes of 2, 5, and 10 cm3, respectively. The combination of 1 micrograms/kg b.w. MTC and 10 Gy irradiation given in three weekly fractions resulted in 21, 28, and 29 days growth delay for the above tumor volumes. The lower effect of combination as compared to irradiation alone is discussed with the flow cytometry data. These data show that early after start of treatment the proportion of tumor cells remains constant in contrast to radiation alone where the fraction of tumor cells decreases because of influx of granulocytes and macrophages into the tumor. In contrast to the reduced effect on tumors the combination treatment was considerably more toxic for the animals than the single treatments.