PTGDR2 and gastric cancer: Zhang et al. [20, 21] showed that PGD2 or PTGDR2 could inhibit the nuclear STAT3 expression and promote its cytoplasmic expression in SGC-7901 and HGC-27 gastric cancer cell lines, thereby inhibiting the self-renewal ability and differentiation of the tumor, as well as inhibiting tumor growth and drug resistance in vivo.