Comparing tumors grown in cPLA2 knockout vs wild-type mice, we demonstrated that prostaglandins (PGE2, PGD2 and PGF2a) were produced by both cancer cells and the tumor microenvironment (TME), but leukotriene (LTB4, LTC4, LTD4, LTE4) production required cPLA2 expression in the TME. The gene discussed is PLA2G4A; the disease is cancer.