IFNγ-induced growth inhibition Rising concentrations of IFNγ for 5 days led to a time- and dose-dependent growth inhibition of neuroendocrine gastrointestinal tumor cells, as measured by crystal violet staining. The growth of BON tumor cells was inhibited with an IC50 value of 135 ± 10 U/ml (A). STC-1 cells displayed an IC50 value of about 100 U/ml (95 ± 15 U/ml) (B). Data are given as percentage of untreated controls (means ± SEM of 4 experiments). *, statistical significance (p < 0.05) compared to untreated controls.