IDO1 and cancer: Finally, we found that multiple immune checkpoints, including IDO1, B7-H3 and PD-L2, were overexpressed in samples in the top quartile of the C-ECM-up score distribution relative to bottom quartile cancers after adjusting for tumour type (2 fold change (FC), FDR < 0.01, Supplementary Data 1), indicating the upregulation of adaptive resistance mechanisms to immune-cell-mediated destruction (Supplementary Figure 3D).