This HTRF cell-based assay conveniently and accurately quantifies phosphorylated STING at Ser366. Following pathogen infection and binding of dsDNA to the cytoplasmic sensor cGAS, STING protein is phosphorylated by TBK1, enabling its binding to IRF3 which induces IFNs type 1 production. The STING pathway is then switched off by STING degradation involving autophagy. In immuno-oncology, activating the STING pathway has shown promising anti-tumor effects in pre-clinical models and thus represents a therapeutic strategy to treat human cancer.