IDO1 and neoplasm: It has been reported that cervical cancer cells with IDO1 expression were mostly found in cells at the invasive front [13] and the high ratio of kynurenine/tryptophan was positively correlated with lymph node metastasis, tumor size and low disease-free survival of cervical cancer patients [14], suggesting that IDO1 may be involved in the progression of cervical cancers.