The purpose of this study is to explore the effect of immunological heterogeneity of tumor microenvironment in the short-term outcome and long-term outcome of patients with gastric cancer.

A prospective cohort study will be performed to explore the effect of immunological heterogeneity of tumor microenvironment in the short-term outcome and long-term outcome of patients with gastric cancer. The evaluation parameters are perioperative clinical efficacy, postoperative complications, and 3-year survival and recurrence rates.

Inclusion Criteria:

1. Age from 18 to 80 years
2. Histology confirmed gastric adenocarcinoma (papillary, tubular, mucinous, signet ring cell, or poorly differentiated) confirmed pathologically by endoscopic biopsy.
3. Clinical stage: cTNM: stage I or above at preoperative evaluation according to the American Joint Committee on Cancer (AJCC) Cancer Staging Manual Eighth Edition
4. Performance status: Eastern Cooperative Oncology Group (ECOG) ≤ 2 (normal to symptomatic but in bed less than half the day)
5. Clinically fit for gastric cancer surgery, i.e. adequate renal, hepatic, hematologic, and pulmonary function.
6. Written informed consent

Exclusion Criteria:

1. Women during pregnancy or breast-feeding
2. Severe mental disorder
3. History of previous gastrectomy, endoscopic mucosal resection, or endoscopic submucosal dissection
4. History of other malignant diseases within the past five years
5. History of unstable angina or myocardial infarction within the past six months
6. History of a cerebrovascular accident within the past six months
7. History of continuous systematic administration of corticosteroids within one month
8. Requirement of simultaneous surgery for other diseases
9. Emergency surgery due to complication (bleeding, obstruction, or perforation) caused by gastric cancer
10. Forced expiratory volume in 1 second (FEV1)<50% of predicted values
11. Inclusion in another clinical trial

Patients who are assigned to undergo gastrectomy for gastric cancer are included.