The average β-values (indicating promoter methylation) for the GPCRs genes were significantly higher in the HNSCC samples than in the normal samples (p < 0.05), except for PTGER4 and TBXA2R. Moreover, we have compared the expression level of the GPCRs genes between HNSCC and normal control using the samples from TCGA database (Supplementary Table S6). The gene discussed is PTGER4; the disease is head and neck squamous cell carcinoma.