IDO1 and central nervous system cancer: Figure 5 shows that IDO, TDO, KAT2, KMO, and QRPT were expressed in low-grade glioma and GBM, confirming our KMO experimental results. Furthermore, the KP enzyme expression in the GBM samples appeared to favor the long arm of the KP, which leads to QUIN and NAD+ production (Figure 5D,E). The GBM patients were further divided into two groups, low KMO and high KMO, according to the median KMO expression. The Kaplan–Meier plot and the log-rank test were used to assess the prognosis in these groups (Figure 5F).