Furthermore, data showed that HSCs promoted G-MDSC expansion via COX2-PGE2-EP4 signaling, and inhibiting HSC-derived PEG2 with a COX-2 inhibitor reduced tumor grow and MDSCs accumulation, which indicated that the PGE2/EP4 pathway was involved in induction of MDSCs by HSCs. The gene discussed is PTGER4; the disease is neoplasm.