Abstract
The purpose of present study is to clarify experimentally significance of tumor heterogeneity. Two sarcomas of # 6107 and #9037 were transplanted into syngeneic C3H male mice. Single cell suspensions for each tumor were mixed together at various ratios just prior to transplantation. When tumors grew to reach 7.5-8.0 mm in diameter, leg tumors were locally irradiated with either Cs-137 gamma rays or 290 MeV/n carbon ions at an LET of 74 keV/microm. Tumor growth (TG) time was obtained by calculating days required for a tumor to reach 5 times initial volume, and Tumor Growth Delay time was used to obtain an isoeffect dose. Tumor control probabilities were calculated by counting number of mice free of tumors 120 days after irradiation. TG time of tumors was identical to each other when the mixture ratio was varied by 11 steps. TG time after transplantation of 100 % #6107 cells was 36 days, and shortened to 28 or 20 days after that of 90 or 50 %. respectively. Tumors after transplantation of lower than 50% #6107 cells showed TG time identical to those after transplantation of 100% #9037 cells. Gamma ray radiosensitivity got higher with an increase of the mixture ratio of #6107 cells. Isoeffect doses for TGD 20 days increased from 15 to 32 Gy when the mixture ratio increased from 0 to 100%. This dose increase was less prominent for TCD50 (50% tumor control dose). We concluded that tumor heterogeneity affected more prominently growth delay than tumor control.
