PTGS1 and neoplasm: To investigate the impact of tumor cell-derived PGE2, MC38 cells deficient COX-1 and COX-2 (encoded by Ptgs1/Ptgs2, termed MC38ptgs-/-) were grafted on the flank of C57BL/6 Kaede mice and the NK cell compartment compared with that of MC38 tumors (Fig. 4B).