PTGS2 and ovarian cancer: It has been demonstrated that MDSCs not only secrete Th17-driving cytokines (IL-1β, IL-6, and IL-23) but also produce NO and Prostaglandin-E2 (PGE2) to facilitate Th17 cells differentiation, which required nitric oxide synthase (NOS) and cyclooxygenase 2 (COX-2) activity, consequently portraying chronic inflammatory state to facilitate tumor growth in oral squamous cell carcinoma and ovarian cancer (41, 42).