In addition, prostaglandin E2 (PGE2), the main product of tumor COX-2, regulates VEGF through EP3 and EP4, which has an important effect on tumor matrix formation and tumor growth, and regulates VEGF-C and promotes lymphangiogenesis in lung adenocarcinoma through EP1 [36, 37]. Here, PTGER1 is linked to lung adenocarcinoma.