Effect of tumor burden on tumor progression. (a) The effects of tumor burden on tumor growth curves were examined using of ectopic tumor in mice implanted with various amounts of tumor cells (1 × 105, 1 × 107, and 1 × 109). The quantitative data are shown, and Y-axis represents the relative ratio, normalized to the tumor size in male mice 3 weeks after implantation with 1 × 105 cells. *, p < 0.05. (b) The effects of tumor burden on the invasive capacity of LNCaP prostate cancer in immunocompromised host were evaluated using orthotopic tumor implantation. The representative slides and quantitative data are shown. (c) The expressions on CD44 and Twist proteins in xenograft tumors implanted with various amounts of tumor cells. Scale bars: 20 μm.