Preoperative Abdominal Enhanced CT, 18F-FDG PET/CT and 68Ga-FAPI PET/CT in Peritoneal Carcinomatosis of Gastric Cancer

This study aims to explore the value of 68Ga-FAPI PET/CT in the diagnosis of gastric cancer peritoneal carcinomatosis in high-risk patients compared with conventional abdominal enhanced CT and 18F-FDG PET/CT. The patients with gastric adenocarcinoma (cT4/N+/M0-1) will be studied.

After being informed about the study and potential risks, all patients giving written informed consent will receive 68Ga-FAPI PET/CT on the 2nd day to 1st week of 18F-FDG PET/CT. On PET/CT, omentum, peritoneum, and mesenteric lesions with increased radioactive uptake are defined as suspicious peritoneal carcinomatosis. The number of these positive lesions, the maximum standardized uptake value (SUVmax), median and range will be recorded. Subsequently, the patients will undergo laparoscopic exploration, and if radical resection is assessed, radical gastrectomy (D2 lymph node dissection) will be performed. If a radical resection is not feasible, for patients with peritoneal carcinomatosis detected, one metastasis will be taken for rapid frozen diagnosis. After the peritoneal carcinomatosis is confirmed, the metastases seen under laparoscopy will be matched with the suspicious peritoneal carcinomatosis on the three preoperative imaging examinations. The intraoperative findings are used as the gold standard to compare the detection efficiency of the three imaging examinations for peritoneal carcinomatosis. Patients with unresected tumors will receive 4 cycles of conversion therapy or neoadjuvant therapy. After the treatment, 18F-FDG PET/CT and 68Ga-FAPI PET/CT will be performed again. If necessary, patients will be subjected to a second laparoscopic exploration, and radical gastrectomy (D2 lymph node dissection) will be performed for appropriate patients. If a radical resection is still not feasible, for patients with peritoneal carcinomatosis detected, biopsy of metastases will be performed if necessary.

Eligibility Criteria:
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. The clinical tumor stage before PET/CT scan was evaluated as cT4/N+/M0-1, according to the American Joint Committee on Cancer (AJCC) Cancer Staging Manual Eighth Edition
4. Performance status of 0 or 1 on Eastern Cooperative Oncology Group scale (ECOG)
5. American Society of Anesthesiology score (ASA) class I, II, or III
6. Written informed consent

Exclusion Criteria:

1. Women during pregnancy or breast-feeding
2. Severe mental disorder
3. History of previous abdominal inflammatory diseases (such as peritonitis, pancreatitis, cholecystitis, inflammatory bowel disease)
4. History of unstable angina or myocardial infarction within past six months
5. History of cerebrovascular accident within past six months
6. History of continuous systematic administration of corticosteroids within one month
7. Emergency surgery due to complication (bleeding, obstruction or perforation) caused by gastric cancer
8. Forced expiratory volume in 1 second (FEV1)\<50% of predicted values
9. History of allergy to tracer agents of PET/CT
10. History of allergy to contrast agents of CT