IDO and TDO, which function to initiate the kynurenine pathway by converting tryptophan to N-formylkynurenine, were proved to contribute to the malignancy of glioma (Du et al., 2020), indicating that activation of kynurenine pathway was a hazardous factor for glioma, in line with our findings. The gene discussed is IDO1; the disease is glioma.