The purpose of this study was to evaluate whether submucosal or subserous injection of indocyanine green during laparoscopic lymphadenectomy for patients with gastric cancer was different. The patients with gastric adenocarcinoma (cT1-4a, N0/+, M0) were studied.

In recent years, with the successful application of ICG (indocyanine green) fluorescence imaging technology in laparoscopic equipment, scholars have found that ICG near-infrared imaging has better tissue penetration and can better identify lymph nodes in hypertrophic adipose tissue than other dyes under visible light, which makes ICG fluorescence imaging guide laparoscopic radical resection of gastric cancer lymph node dissection has become a new exploration direction. ICG near-infrared imaging technology has important research value, good application prospects, and broad development space in laparoscopic radical resection of gastric cancer. However, at present, the application of ICG near-infrared imaging technology in laparoscopic radical resection of gastric cancer is still in the exploratory stage, and there is no unified standard. Therefore, in the world, there is still a lack of high-level evidence-based evidence of large-sample prospective randomized controlled trials to evaluate the effectiveness, safety, and feasibility of submucosal or subserous injection of ICG in guiding laparoscopic D2 resection of gastric cancer. The investigator first carried out this study in the world to evaluate the lymph node dissection and perioperative safety of gastric cancer patients who received a submucosal injection of ICG and subserous injection of ICG during laparoscopic radical gastrectomy in the same period, to promote the standardized development of ICG near-infrared imaging in laparoscopic radical gastrectomy.

Inclusion criteria:

1. Age from 18 to 75 years
2. Primary gastric adenocarcinoma (papillary, tubular, mucinous, signet ring cell, or poorly differentiated) confirmed pathologically by endoscopic biopsy
3. Clinical stage tumor T1-4a (cT1-4a), N0/+, M0 at preoperative evaluation according to the American Joint Committee on Cancer (AJCC) Cancer Staging Manual Eighth Edition. Preoperative staging was made by conducting mandatory computed tomography (CT) scans and an optional endoscopic ultrasound
4. No distant metastasis, no direct invasion of pancreas, spleen or other organs nearby in the preoperative examinations
5. Performance status of 0 or 1 on Eastern Cooperative Oncology Group scale (ECOG)
6. American Society of Anesthesiology score (ASA) class I, II, or III
7. Written informed consent

Exclusion criteria:

1. Women during pregnancy or breast-feeding
2. Severe mental disorder
3. History of previous upper abdominal surgery (except laparoscopic cholecystectomy)
4. History of previous gastrectomy, endoscopic mucosal resection or endoscopic submucosal dissection
5. Rejection of laparoscopic resection
6. History of allergy to iodine agents
7. Enlarged or bulky regional lymph node diameter over 3cm by preoperative imaging
8. History of other malignant disease within past five years
9. History of previous neoadjuvant chemotherapy or radiotherapy
10. History of unstable angina or myocardial infarction within past six months
11. History of cerebrovascular accident within past six months
12. History of continuous systematic administration of corticosteroids within one month
13. Requirement of simultaneous surgery for other disease
14. Emergency surgery due to complication (bleeding, obstruction or perforation) caused by gastric cancer
15. Forced expiratory volume in 1 second (FEV1)<50% of predicted values
16. Linitis plastica, Widespread

Although it was not feasible to blind the surgeons and participants, the pathologists were unaware of the intervention received by the patients. The researcher performing the statistical analyses was blinded to the patient group allocation.