Although the M1/M2 nomenclature is an oversimplification of the actual complexity of the brain microenvironment, the M1 phenotype is functionally distinguished by its ability to eliminate pathogens and tumor cells, secrete pro-inflammatory cytokines, such as IL-23, IL-12, IL-6, IL-1β, and TNFα, and produce reactive oxygen species (ROS). The gene discussed is TNF; the disease is neoplasm.