We observed a significant (p < 0.0001) increase in the expression of IDO1, KYNU, and QPRT genes involved in the kynurenine pathway, in PD and TN cancer cells (Figure 3K; Figure S3P; Table S2) Expression of these genes can result in immunosuppressive behavior (Triplett et al., 2018) indicating that cancer cells within PD tumors may directly inhibit the activity of the immune system. This evidence concerns the gene IDO1 and cancer.