CD4 and adenoma: The frequency of CD4+CD25+ Treg cells gradually increased from early to advanced adenomas and finally to CRC, suggesting that Treg cells increased to exert immunosuppressive effects as adenomas progressed toward CRC (grade I vs. grade II, 0.63 vs. 5.30, P = 0.0400; grade I vs. grade III, 0.63 vs. 19.6, P < 0.0001; grade I vs. CRC, 0.63 vs. 29.9, P < 0.0001; grade II vs. CRC, 5.30 vs. 5.30, P = 0.0059).