IDO1 and breast cancer: Contrary to the positive correlation between IDO1 and TILs in most studies (Zhai et al., 2015) and the expression of IDO1 indicating a good NAC response in BC, other studies (Salvador-Coloma et al., 2020) have shown that IDO1 is positively correlated with early myeloid–derived suppressor cells (eMDSCs) and has a poor NAC response, which may be related to the different influences of IDO1 expression in tumor cells and immune stromal cells on prognosis.