Effect of genistein and radiation treatment on the survival fraction of human tumor cell lines. (A) PC-3 prostate cancer cells were treated with 15 μmol/L genistein for 24 hr then irradiated with 2 or 3 Gy photons. After radiation, cells were plated in a clonogenic assay. (B) Cells from the PC-3 (prostate cancer), BR-231 (breast cancer), and KCI-18 and RC-2 (renal cell carcinoma) cell lines were treated with 15 μmol/L genistein for 24 hr then irradiated with 3 Gy photons and plated in a clonogenic assay. Colonies were stained with crystal violet and counted after 11–13 days incubation. The mean survival fraction ± S.E.M. of triplicate wells was normalized to control cells based on plating efficiency. (*): value statistically significant from control at p < 0.05. Combined treatment was significantly greater (p < 0.05) than genistein or radiation alone.