NOS2 and neoplasm: Photodynamic therapy (PDT) is a promising minimally invasive approach for tumor treatment that induces apoptosis by converting O2 molecules into reactive oxygen species (ROS) with high efficiency.[11] L‐arginine (L‐Arg), a natural and biocompatible nitric oxide (NO) precursor, serves as the substrate for nitric oxide synthase (NOS) to generate NO.