Phase II Clinical Study of PD1 Antibody (SHR-1210) Combined With Trastuzumab, Oxaliplatin and Capecitabine for Neoadjuvant Therapy of Gastric Adenocarcinoma/Gastroesophageal Junction Adenocarcinoma

• Signed the informed consent form

• 18-75 years old

• Pathologically confirmed gastric adenocarcinoma or gastroesophageal junction adenocarcinoma (cT4 or / and N+M0, MDT believes that perioperative treatment is required):

∙ No peritoneal metastasis in CT

‣ evaluated as a resectable lesion. Note: Whether there is a distant metastasis should be confirmed by CT or MR scan. If bone metastasis is suspected, a bone scan should be performed. If there is suspected peritoneal metastasis, a laparoscopy should be performed. If brain metastasis is suspected, CT or MR examination should be performed.

• Have not received cytotoxic chemotherapy or targeted therapy and local tumor resection

• HER2 immunohistochemistry 3+ and fluorescence in situ hybridization showed significant amplification

• ECOG≤1

• Tumor specimens that can be used to detect PD-L1 and MSI status can be provided. Detection of PD-L1 and MSI will be performed after enrollment. This test requires patients to provide paraffin-embedded biopsy specimens.

• White blood cells ≥ 4×109/L, platelets without blood transfusion ≥ 100×109/L, absolute neutrophil count (ANC) ≥ 1.5×109/L without granulocyte stimulating factor, hemoglobin ≥ 90 g/L

• bilirubin ≤ 1.5 times the upper limit of normal value, cereal grass and alanine aminotransferase ≤ 2.5ULN. If there is liver metastasis, the grass and alanine aminotransferase ≤ 5ULN.

⁃ serum creatinine ≤ 1.5ULN, or GFR \> 45 ml / min

⁃ serum albumin ≥ 25 g / L (2.5 g / dL)

⁃ INR or APTT ≤ 1.5 ULN

⁃ Hepatitis B surface antigen positive patients need to detect hepatitis B DNA virus quantitative detection, only patients below the upper limit of normal detection can be enrolled, and long-term use ofanti-hepatitis B virus drugs