PTGS1 and neoplasm: We further validated that BRAFV600E melanoma depended on tumour-derived PGE2 to evade anticancer immunity by demonstrating that COX-deficient Ptgs1/Ptgs2−/− BRAFV600E melanoma, which lacks PGE2 production, failed to escape immune control (Fig. 1a and Extended Data Fig. 2a).