Hybrid F98:F98CD spheroids with constant number of F98 cells (4×103) and increasing number of prodrug converting F98CD cells (100, 200,400) incubated with a) 5-FC 0.1 μg/ml, b) 5-FC 0.2 μg/ml, c) 5-FC 0.4 μg/ml. The growth kinetics, calculated at 2, 7 and 14 days of incubation as a % of control values at day 14 are shown. Mean of 3 experiments, error bars denote standard errors. Asterisks (*) denote significant differences (p<0.05) compared to control value.