D2HGDH and head and neck squamous cell carcinoma: Numerous studies [6, 10, 11] have demonstrated that the occurrence and development of HNSCC are closely associated with the mutation and abnormal expression of genes, which include Six genes (PEX11A, NLRP2, SERPINE1, UPK, CTTN, D2HGDH) signature, and mutations in 4 genes (KL, CCR7, LGR5, RORB) are associated with prognosis of HNSCC.