Background. Peritoneal carcinomatosis is a frequent and deadly localization of gastric cancer. Available imaging techniques have a low accuracy in detecting small peritoneal nodules, and direct laparoscopic visualization may fail too. A more accurate staging technique would be advantageous for individualization of therapeutic path. Indocyanine Green (ICG) fluorescence imaging has been reported as a tool for visualizing small peritoneal seedings due to the "enhanced permeability and retention" (EPR) effect of cancer nodules.

Aim. To explore the feasibility and effectiveness of fluorescence-enhanced peritoneal carcinomatosis detection in patients with gastric cancer undergoing staging laparoscopy.

Methods. This prospective, multicentric, single arm study will include patients with gastric cancer, without a radiological suspicion of peritoneal carcinomatosis, undergoing staging laparoscopy. An intravenous injection of ICG is given at different dosage and at different timepoints before the intervention. During the staging laparoscopy, the abdominal cavity exploration is performed using standard white-light, and subsequently using fluorescence imaging. Suspicious nodules are harvested, until a maximum of 5 per patient, and sent for definitive histological examination. Peritoneal washing is also harvested for cytologic assessment in all cases. The eventual benefit of fluorescence imaging in terms of additional peritoneal lesions that were not detected during standard white-light imaging is evaluated.

Discussion. This study will establish if fluorescence imaging increases sensitivity and/or specificity of staging laparoscopy in detecting peritoneal carcinomatosis from gastric cancer. Improved accuracy may translate in better care path selection.

Inclusion Criteria:

1. Age of ≥18years
2. Ability to provide written informed consent
3. Histologically confirmed gastric adenocarcinoma or oesophago-gastric junction adenocarcinoma Siewert 2 and 3
4. cT>1
5. cM0 (clinical staging: no metastases)
6. Staging laparoscopy is indicated by the internal work-up protocol
7. Staging laparoscopy is in accordance with NCCN (National Comprehensive Cancer Network) guidelines

Exclusion Criteria:

1. Pregnancy
2. Iodine allergy/sensibility
3. Clinical P1 (defined as high probability of peritoneal carcinomatosis at imaging)
4. Investigator judgement that the patient should not participate for any reason