NFE2L2 and head and neck squamous cell carcinoma: NRF2 up-regulates the pentose phosphate pathway (PPP) enzyme, glucose-6-phosphate dehydrogenase (G6PD) and transketase (TKT) mediated nucleotide biosynthesis, thereby promoting the malignant progression of head and neck squamous cell carcinoma (HNSCC) (26).