GPR18 and head and neck squamous cell carcinoma: Importantly, the GPR18 mRNA levels were prognostic among HPV(+)HNSCC patients (HR = 0.634, P = 0.0355), superior to TIL-B, MS4A1 mRNA, and CD20 protein levels, which were not prognostic in HPV(+)HNSCC at all (Fig. 3f).