PTGER4 and cancer: Using PGE2 receptor antagonists EP2 (AH6809) and EP4 (AH23848) to block PGE2 receptors EP2 and EP4 can inhibit the nuclear accumulation of p50, reprogram M-MDSCs to a less suppressive phenotype, restore the anti-tumor activity of IFN-γ, and enhance the efficacy of cancer immunotherapy 96.