IDO1 and breast neoplasm: Most researches on MRC2 to date have focused on its role in the development of cancer, as it can promote breast tumor growth,17 co-operate with the matrix metalloproteinase to remodel of extracellular matrix that attenuate renal fibrosis,28 and predict prognosis of hepatocellular carcinoma18 and prostate cancer.29 Besides, MRC2 is also closely related to collagen turnover.30 In our study, we found that both estrogen and 1-MT promoted the expression of MRC2 in ESCs, which indicates that MRC2 is downstream to estrogen and IDO1.