The genetically-encoded red fluorescent protein (KillerRed) leads to irreversible DNA damage and cell killing via an apoptotic pathway upon irradiation with a narrow light bandwidth of 520–590 nm due to formation of highly-cytotoxic levels of ROS15, 16; offering additional options in treatment of tumour and study of tumour radiosensitization. The gene discussed is TNFRSF10B; the disease is neoplasm.