Tumorigenicity of R2d and R2N1d cells, and genes expressed by tumors developed by R2N1d cells. A, the development of tumors in immune-deficient mice after inoculation with different numbers of R2d or R2N1d cells (1 × 105, 1 × 106 or 1 × 107 cells per site) for 4 months (R2d) or 4 weeks (R2N1d). The average size of tumors for each treatment are also determined. B, histological sections of resected tumor revealed sheets of polygonal cells with high nucleus/cytoplasm (N/C) ratio. C, these tumor cells expressed Ki67 (90%), VEGF (score 4), COX-2 (score 4) and MMP-9 (score 4). The length of the scale bar of these photos is 100 μm.