ENPP1 and head and neck squamous cell carcinoma: Multiple logistic analysis and ROC analysis on the combined expression profile of these genes with significant AUC value (Table S2) identified a diagnostic signature (NAMPT, ENPP1, SIRT1, and PARP1) able to discriminate grade 1 from grade 2 HNSCC (AUC = 0.7259; p < 0.0001).