Gastric cancer can be staged according to the degree of invasion of cancer cells to the body of stomach and whether there is lymphatic metastasis or distal metastasis, and clinically it can be classified into Stage I, Stage II, Stage III and Stage IV mainly according to TNM staging method. T mainly represents the situation of the primary tumor and is divided into T1, T2, T3 and T4. T1 represents that the cancer lesion is light to the mucosa or relatively superficial to the submucosa; T2 represents that the cancer lesion is in the plasma membrane or muscularis propria; T3 represents that the lesion has already penetrated the plasma membrane layer and invaded the surrounding tissues; T4 represents that the lesion has already involved the esophagus or the duodenum. N mainly represents the extent of regional or lymph node metastasis, which is further divided into N1, N2, and N3. N1 represents 1-2 regional lymph node metastasis, N2 represents 3-6 regional lymph node metastasis, and N3 represents more than 7 regional lymph node metastasis. M mainly represents distant metastasis and is currently categorized as M0 and M1. M0 represents no distant metastasis and M1 represents the presence of distant metastasis.