Characterization of KGN cells at different passages. (A) Morphology of KGN cells at Days 1 and 4 (P9 vs. P58). (B) Population doubling measured for 4 days using the early and advanced passage KGN cells seeded at 2 × 105 cells/dish (P9 vs. P58). (C, D) Invasiveness of different passage KGN cells (P6 vs. P53). Cells in serum-free medium at a concentration of 1 × 105 cells/well were subjected to an invasion assay using transwell chambers coated with Matrigel for 12 h (C; normal cells, D; Mitomycin C-treated cells). The proliferation of Mitomycin C-treated cells was blocked, as determined by the TetraColor One proliferation assay. All experiments were triplicated and the data are shown as the mean number with SEM. Statistical difference was analysed by Student's t-test (*P < 0.05).