To understand the role of cancer-cell-derived PGE2 in immune evasion, we ablated PGE2 production through cyclooxygenase-1 (COX1; encoded by Ptgs1) and COX2 (encoded by Ptgs2) KO in RTT cells and engrafted them into Rag2–/– mice. The gene discussed is PTGS1; the disease is cancer.