Patients with higher 1‐month post‐operative ctDNA levels demonstrated shorter overall survival status (hazard ratio [HR] = 5.30, p = 0.0022) and a higher risk of recurrence (HR = 3.85, p = 0.011). The model combining ctDNA with conventional serum tumor markers for GC, including carcinoembryonic antigen, carbohydrate antigen 19‐9, and CA72‐4, shows high predictive effectiveness for GC prognosis with an area under the curve of 0.940 (p = 0.002), which is higher than net ctDNA and other models without ctDNA. This evidence concerns the gene CEACAM5 and gastric cancer.