In the Phase 2 clinical trial that utilized ADU-S100 (a STING-agonist that functions as a synthetic cyclic dinucleotide) co-administered to patients with PD-L1 positive recurrent or metastatic HNSCC, the endpoints of the study were patient safety, preliminary anti-tumor activity, pharmacokinetics, and immunomodulation [66,69]. Here, STING1 is linked to head and neck squamous cell carcinoma.