Patients with metastatic or unresectable gastric cancer are usually given 5-fluorouracil (5-FU) and platinum-based chemotherapy, but patients with advance disease usually have a poor prognosis. The use of chemotherapy increased the levels of cyclooxygenase-2 in tumor cells, which in turn increase the levels of prostaglandin E2 (PGE2) in the tumor microenvironment. When PGE2 binds to their receptors EP1 to EP4 on immune cells, it triggers an immunosuppressive tumor microenvironment. The use of the EP2 and EP4 dual antagonist OCT-598 was tested in the preclinical setting for gastric cancer.