IDO1 and neoplasm: To explore the possibility of multiplexed analysis of a broader group of protein regulators of the tumor-immune interface, we configured PRM assays for the immune checkpoint proteins indolamine-2,3-dioxygenase 1 (IDO1), lymphocyte activating 3 (LAG3), hepatitis A virus cellular receptor 2 (HAVCR2 (TIM-3)), chromosome 10 open reading frame 54 (C10orf54 (VISTA)), and CD40 molecule (CD40).