This study intends to explore the value of 68Ga-FAPI-04 and 18F-FDG PET/CT in the evaluation of treatment response to neoadjuvant chemotherapy(NAC) for patients with locally advanced gastric cancer(LAGC).

Before the start of NAC, baseline 68Ga-FAPI-04 PET/CT and 18F-FDG PET/CT scans will be scheduled in all enrolled patients. Next, the patients with resectable LAGC will receive NAC treatment, surgery will follow 3~6 weeks after finishing NAC. Abdomen 68Ga-FAPI-04 PET/CT and 18F-FDG PET/CT will be scheduled after one cycle of NAC treatment or before surgery. Imaging response measurements will be compared with the histopathological tumor regression grade (TRG) of the resection specimen as gold standard.

Inclusion criteria

1. Age between 18-75 years.
2. Histologically confirmed gastric adenocarcinoma through gastroscopy.
3. Resectable gastric cancer.
4. ECOG performance status 0-1.
5. White blood count >4x109/L, Absolute neutrophil count (ANC) >2x109/L, Hemoglobin (Hb)>90g/L, Platelets >100x109/L.
6. Ejection Fraction>50%.
7. Serum bilirubin <1.5x ULN; ALT and AST <1.5x ULN.
8. Serum creatinine ≤1.5x ULN, or GFR> 60ml/min.
9. Agreement to participate in this study with informed consent form.
10. Willingness and ability to comply with the protocol for the duration of the study.
11. No children bearing petential in the next six months before enrollment.

Exclusion criteria

1. With second primary malignant diseases in past five years, exceptions include basal cell and squamous cell carcinoma of the skin that have been cured.
2. Known hypersensitivity reaction to chemotherapy drugs or with contraindications.
3. With severe disease or other unsuitable conditions determined by investigators. Inadequate organ function.
4. With uncontrollable diabetic or fasting blood glucose level ≥11 mmol/L on the test-day.
5. With severe mental symptoms, unconscious or unable to complete the examination.
6. Pregnancy or possibly pregnant woman, breastfeeding woman.
7. Lack of compliance.