PTGER4 and gastric cancer: The implementation of methylation detection technologies in cancer research is still in its early stages, and only a few blood-based tools have been approved for clinical diagnostic application by the FDA or NMPA (in China), such as the Septin9 gene methylation assay for colorectal cancer, the RNF180/Septin9 gene methylation assay for gastric cancer, or the SHOX2/RASSF1A/PTGER4 gene methylation assay for lung cancer.