Neoadjuvant Nab-Paclitaxel Plus Oxaliplatin, S-1, and Sintilimab in Early-Onset Resectable Gastric Cancer

Prior treatment

• Prior treatment for gastric cancer with cytotoxic chemotherapy, radiotherapy, or immunotherapy;
• Currently receiving systemic corticosteroids or other immunosuppressive therapy;
• Prior organ transplantation or use of anti-rejection medications;
• Use of any investigational drugs within 4 weeks prior to study enrollment.

Other illness

• Patients with HER-2 positive gastric cancer, as determined by immunohistochemistry (IHC) or fluorescence in situ hybridization (FISH);
• History of other malignancies within the past 5 years;
• Active autoimmune diseases, including but not limited to systemic lupus erythematosus, rheumatoid arthritis, myasthenia gravis;
• Active inflammatory bowel diseases, such as Crohn's disease or ulcerative colitis;
• Active tuberculosis, HIV infection, or severe active hepatitis B or C;
• History of uncontrolled epilepsy, central nervous system disorders, or psychiatric illnesses that, in the investigator's judgment, may interfere with informed consent or compliance with oral medication;
• Clinically significant (active) cardiac diseases, including symptomatic coronary artery disease, NYHA class II or above congestive heart failure , severe arrhythmias requiring medical intervention, or myocardial infarction within the past 12 months;
• Severe uncontrolled recurrent infections or other uncontrolled serious comorbidities;

Other

• Participants meeting any of the following criteria will be excluded:
• Patients with dMMR (deficient mismatch repair) or MSI-H (microsatellite instability-high) tumors, as determined by IHC;
• Pregnant or breastfeeding women;
• Presence of upper gastrointestinal obstruction that may impair the oral intake or absorption of S-1;

• Participants must meet all of the following inclusion criteria:
• Male or female, aged ≥16 and ≤45 years;
• Karnofsky performance score ≥70% or ECOG performance status 0-1;
• Histologically confirmed adenocarcinoma of the stomach or gastroesophageal junction (GEJ).
• For gastric body cancer: clinical stage cT3-T4a N+ M0;
• For GEJ cancer: clinical stage cT2-T4a N+ M0;
• For cT4b Nany M0 cases: location may be gastric body or GEJ.
• Staging is based on contrast-enhanced CT, MRI (if needed), and endoscopic ultrasonography (EUS) (if needed);
• Assessed as resectable after multidisciplinary team (MDT) discussion;
• Surgical evaluation confirms that D2 radical gastrectomy is feasible;
• Sufficient physical condition and organ function to tolerate major abdominal surgery;
• Baseline laboratory tests meet the following criteria:
• Hemoglobin ≥90 g/L
• Absolute neutrophil count (ANC) ≥1.5×10⁹/L
• Platelets ≥100×10⁹/L
• ALT and AST ≤2.5× upper limit of normal (ULN)
• Alkaline phosphatase (ALP) ≤2.5× ULN
• Total bilirubin \<1.5× ULN
• Serum creatinine \<1× ULN
• Serum albumin ≥30 g/L
• No severe comorbidities that may limit life expectancy to \<3 years;
• Participant is willing and able to comply with the study protocol during the study period;
• Written informed consent must be signed before screening. Participants must understand their right to withdraw at any time without any loss of benefits;
• Willing to provide blood and tissue samples.