We found that only the tumor cell-associated IDO, represented by low IDO intensity, strongly correlates with PD-L1 surface expression (p = 0.0006) and, in consequence, that the number of IDO+ tumor cells directs the intratumoral expression level of the immunosuppressive molecule PD-L1 (p = 0.00015, Table 2). The gene discussed is IDO1; the disease is neoplasm.