Objective: To evaluate the impact and cost-effectiveness of FDG-PET/CT (PET) and diagnostic laparoscopy (DLS) in addition to initial staging by CT and gastroscopy in patients with advanced gastric cancer.

Hypothesis: The study hypothesizes that performing DLS and PET for advanced gastric adenocarcinomas results in a reduction in the number of futile gastrectomies performed and a favorable cost-effectiveness. According to the literature, in 27% of patients a futile gastrectomy can be prevented, and the annual cost-reduction is an estimated €916.438.

Study design: The study design is a prospective observational study. Study population: The study population consists of patients with a surgically resectable, advanced gastric adenocarcinoma (cT3-4a,N0-3,M0), that are scheduled for treatment with curative intent after initial staging with gastroscopy and CT.

Usual care / comparison: Both PET and DLS were recently included in the new Dutch guidelines for the treatment of gastric cancer, as staging modalities for advanced (T3-4) tumors after initial staging. The costs of the study population will be compared to retrospective data of patients who underwent curative surgery (gastrectomy) after initial staging with CT alone.

Outcome measures: The primary outcome of this study will be the proportion of patients in whom the PET or DLS lead to a change in treatment strategy. The accuracy of each modality will be analyzed separately. Secondary outcome parameters will be diagnostic performance, morbidity and mortality, quality of life, cost-reduction and cost-effectiveness.

Sample size: Based on the expectation that 22% of patients will have a change in treatment strategy, at least 239 patients will be needed for this study to demonstrate that the diagnostic modalities in the new guideline are break-even. Approximately 543 patients will be eligible for the study in 36 months.

Cost-effectiveness analysis: A state-of-the-art cost-effectiveness analysis and budget impact analysis will be performed on the additive value of PET and DLS by both prospective and retrospective data collection

Inclusion Criteria:

• Histologically proven adenocarcinoma of the stomach or esophagogastric junction (Siewert II and III), by gastroscopy.
• Underwent evaluation with computed tomography (CT) of the abdomen and chest.
• Surgically resectable, advanced tumor (cT3-4a,N0-3,M0), as determined by a multidisciplinary team meeting. An advanced tumor is defined as a transmural tumor with an irregular outer margin, objectified on CT.
• Intention to perform a curative gastrectomy

Exclusion Criteria:

• Siewert type I esophagogastric junction tumor
• Unfit or unwilling to undergo surgery

The study population consists of patients with a surgically resectable, advanced gastric adenocarcinoma (cT3-4a,N0-3,M0), that are scheduled for treatment with curative intent after initial staging with gastroscopy and CT.