6PGD is known as a key enzyme in PPP flux, which is involved in metabolizing 6-phosphogluconate (6-PG) to ribulose-5-phosphate (Ru-5-P), and emerging evidence has revealed that the up-regulation of 6PGD expression or enzyme activity serves as a contributor to lung cancer, thyroid cancer, colon cancer, head and neck cancer, and ovarian cancer. The gene discussed is PGD; the disease is head and neck cancer.