Considering genes with AUC > 0.7 and p ≤ 0.0001, we found 6 genes for HNSCC (AOX1, NMNAT2, ENPP3, NADK, CD38, and PARP1), 11 genes for LuSCC (AOX1, NNMT, NMNAT2, NMNAT3, ENPP2, ENPP3, NMRK2, NADSYN1, SIRT1, CD38, and PARP1), and 11 genes for CeSCC (AOX1, NMNAT3, ENPP1, ENPP2, ENPP3, NMRK2, PNP, NADSYN1, SIRT1, SIRT3, and CD38) with a good ability to differentiate each SCC from control samples (Tables S2–S4 and Figure S3). The gene discussed is NADK; the disease is head and neck squamous cell carcinoma.