NOS2 and cancer: MDSCs enhance the progression of various types of tumors by promoting immune suppression, cancer-associated fibroblasts (CAF) activation, angiogenesis, and tumor growth and metastasis [10] via the expression of co-inhibitory receptors, such as PD-L1, and the release of a vast array of molecules, such as arginase-1, inducible nitric oxide synthase (iNOS), nitric oxide (NO), and reactive oxygen/nitrogen species (ROS/RNS) [11, 12].