T: primary tumor; TX: primary tumor could not be evaluated (including incomplete information, no records, etc.); T0: no evidence of primary tumor; Tis: carcinoma in situ, intraepithelial carcinoma not infiltrating the lamina propria; T1: tumor infiltrating into the lamina propria or submucosa; T2: tumor infiltrating into the muscularis or subplasma layer; T2a: tumor invading the muscularis; T2b: tumor invading the subplasma layer; T3: tumor penetrating the plasma membrane layer without invading adjacent structures. When the tumor may have penetrated the muscular layer with invasion of gastrocolic ligament, hepatogastric ligament or large and small omentum, but did not penetrate the visceral peritoneum of these tissues, it is still classified in T2, or T3 if the tumor penetrated the visceral peritoneum covered by these organs; T4: the tumor directly invaded adjacent structures. The adjacent structures of stomach include: spleen, transverse colon, liver, diaphragm, pancreas, abdominal wall, adrenal gland, kidney, small intestine and retroperitoneum. Note: Tumor extends from the stomach wall to the duodenum or esophagus, as determined by the depth of the most severe infiltration including the stomach T. N: localized regional lymph nodes. NX: regional lymph nodes could not be assessed; N0: no regional lymph node metastasis; regardless of the total number of lymph nodes resected and examined, if all lymph nodes are metastasis-free, locate PN0; N1: 1 to 6 regional lymph node metastasis; N2: 7 to 15 regional lymph node metastasis; N3: greater than 15 regional lymph node metastasis. M: distant metastasis. MX: distant metastases could not be assessed; M0: no distant metastases were found; M1: distant metastases were present (including lymph node involvement in the hepatoduodenal ligament, posterior pancreas, mesenteric root and parietal abdominal aorta).