Among 54 GC patients with positive THBS1 methylation in PPLF samples, 72.2% (39/54) patients showed positive PPLF cytology, and 97.1% (33/34) patients with both positive cytology and THBS1 methylation in tumor tissues showed THBS1 methylation in paired PPLF samples. The gene discussed is THBS1; the disease is gastric cancer.