Tumorigenicity of H1650 and H1650-ER1 cells was examined in vitro by a soft agar assay. Dissociated cells resuspended in 0.35% agar were plated on 5% agar and the number of colonies counted after 15 days. (A) Images showing the colonies formed by H1650 and H1650-ER1 cells. The scale bar corresponds to 20 μm. (B) Quantification of colonies formed from 2500 cells in each well. The resistant subline formed a significantly higher number of colonies (p-value < 0.05). The error bars represent s.e.m. (n = 3).