Molecular Evaluation of Neoadjuvant Chemotherapy for Locally Advanced Gastric Cancer

Inclusion Criteria:

1. Ambulatory males or females, age ≥ 18 years
2. Karnofsky Performance Score (KPS) ≥70% or ECOG performance status: 0 or 1
3. Pathologically confirmed gastric adenocarcinoma (regardless of degree of histologic differentiation) or adenocarcinoma with signet-ring cell carcinoma , mucinous adenocarcinoma
4. Clinical Preoperative Stage cT4a/T4bN+M0 disease, including T4b、Bulky-N2, confirmed by CT/EUS
5. Adequate organ function as defined below: Hemoglobin ≥ 9 g/dl, Hematologic Absolute Neutrophil Count （ANC） ≥ 1.5\*109/L, Platelets ≥ 100\*109/L, Aspartate Aminotransferase（AST） and Alanine Aminotransferase(ALT)≤ 2.5×ULN, Alkaline pPosphatase( ALP) ≤ 2.5×ULN, Total Bilirubin （TBIL）≤ 1.5×ULN, Renal Serum Creatinine \< 1.5 ULN, Serum Albumin ≥ 30g/l.
6. No serious concomitant disease that make survival period \< 5 years
7. No pleural effusion, no ascites exceeding the pelvis and no metastasis to the peritoneum, liver or other distant organs are confirmed by abdominal pelvic CT.
8. Planning to undergo gastric cancer D2 surgery after neoadjuvant chemotherapy
9. No prior antitumor treatment is allowed, including chemotherapy, radiotherapy, immune therapy or target therapy
10. No mechanical obstruction.
11. Negative serum or urine pregnant test within 7 days prior to randomization for child-bearing age women
12. Sexually active males or females willing to practice contraception during the study until 30 days after end of study.
13. Subjects has to voluntarily join the study and sign the Informed Consent Form for the study

Exclusion Criteria:

1. Female in pregnancy or lactation, or refuse to receive Contraception measures during chemotherapy
2. With distant metastasis or peritoneal dissemination diagnosed by CT/EUS
3. Underwent prior antitumor treatment, including chemotherapy, radiotherapy, immune therapy or target therapy
4. Serious uncontrolled intercurrent infections or other serious uncontrolled concomitant disease or condition that would make the subject inappropriate for study participation or any serious medical disorder that would interfere with the subject's safety (including current active hepatic, biliary, renal, respiratory disease, uncontrolled diabetes hypertension et al)
5. Clinically serious cardiac disease or pulmonary dysfunction.
6. Patients require emergency surgery with complications (bleeding, perforation and obstruction) caused by gastric cancer
7. Other complications that cause no radical resection
8. Serious concomitant disease that make survival period \< 5 years
9. No detection of CTCs or ctDNA in peripheral blood samples before NCT be enrolled in other clinical trials
10. Allergic reaction to S-1 or oxaliplatin
11. Abnormal GI tract function
12. Refuse to provide blood/tissue sample
13. Sexually active males or females refuse to practice contraception during the study until 30 days after end of study.
14. Person with no capacity (legally) or inappropriate to continue study treatment for ethics/medical reasons.
15. Other situation to be judged not adaptive to the study by investigators