IDO1 and breast cancer: The positive rates of IDO expression in histological grade I, histological grade II, and histological grade III breast cancer were 22.00, 70.00, and 75.00%, respectively (P < 0.05), while the mean MVD levels were 8.26 ± 1.76, 9.41 ± 1.48, and 10.17 ± 1.86, respectively (P < 0.05) (Table 2).