Our key findings are: (1) PTE induces ROS-dependent DNA damage, cell cycle arrest, and apoptosis; (2) PTE activates the STING/TBK1/IRF3 pathway in a ROS-dependent manner; (3) Genetic and pharmacological inhibition of STING attenuates PTE’s effects, establishing its necessity; (4) PTE inhibits tumor growth in xenograft models; and (5) In an immunocompetent model, PTE enhances CD8+ T cell infiltration and function while reducing immunosuppressive populations. The gene discussed is CD8A; the disease is neoplasm.