IDO1 and breast cancer: Our conclusion is consistent with the study of Mansfield et al. using 47 cases of breast cancer samples, including 25 invasive ductal carcinoma and 18 invasive lobular carcinoma, where IDO+ sentinel lymph nodes accompanied by infiltration of Foxp3+ Tregs imply lymph node metastasis of breast cancer, and are therefore regarded as a negative prognostic factor [12].