Fig. 2. IFN- inhibits the growth of MCF-7 and MDA-MB-231 cells in monolayer culture. MCF-7 cells were cultured in SFM plus 0.25% serum, and MDA-MB-231 cells were cultured in SFM alone. IFN- (10 ng/ml) was added, and growth was determined by MTT assay at days 0, 2, and 4. Each point represents the mean of triplicate samples ± SE. Asterisks represent statistically significant differences due to IFN-. *, P < 0.002; **, P < 0.001.