Envafolimab Combined With Chemotherapy in Metastatic or Recurrent Gastric Adenocarcinoma

The objective is to investigate the efficacy and safety of Envafolimab combined with chemotherapy in the treatment of metastatic or recurrent gastric adenocarcinoma.

Envafolimab indication: Envafolimab is the world's first subcutaneous injection of PD-L1 monoclonal antibody.Suitable for adult patients with advanced solid tumors with unresectable or metastatic microsatellite highly unstable (MSI-H) or mismatch repair gene defects (dMMR).

Eligibility Criteria:
Inclusion Criteria:

* 18-75 years；
* ECOG 0-1；
* life expectancy of at least 3 months；
* Negative for HER2 gene expression by central laboratory ；
* The tumor expresses PD-L1 as detected by the central laboratory, and the tumor proportion score (CPS) ≥ 1；
* At least one measurable objective tumor lesion by spiral CT examination, the maximum diameter ≥ 1cm（according to RECIST 1.1）；
* Diagnosed by histology and/or cytology, and assessed by imaging (refer to RECIST 1.1) as advanced metastatic gastric adenocarcinoma or gastric adenocarcinoma that has recurred after previous gastric cancer surgery;
* Not received systemic chemotherapy in the past. Patients who have previously received fluorouracil monotherapy or fluorouracil-based adjuvant therapy or neoadjuvant therapy, and patients who have completed adjuvant therapy or neoadjuvant therapy before the start of the chemotherapy regimen in this trial 6 months ago can be included in this trial. In cases of metastatic disease requiring local remission, remission therapy with radiosensitizing doses of fluorouracil or capecitabine alone is permitted only ；
* satisfactory main organ function，laboratory test must meet the following criteria: hemoglobin (HGB) ≥90g/L, neutrophil count（ANC） ≥1.5×109/L, platelet count（PLT） ≥80×109/L, Serum creatinine（CR）≤1.5 upper normal limitation (UNL)，total bilirubin (TBil) ≤1.5 upper normal limitation (UNL), alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤2.5 UNL (For patients with liver metastasis, the AST/ALT must be ≤5.0 UNL), Activated partial thromboplastin time (APTT), international normalized ratio (INR), prothrombin time (PT) ≤ 1.5×ULN; left ventricular ejection fraction (LVEF) ≥ 50%; thyroid stimulating hormone (TSH) within the normal range Within: if the baseline TSH exceeds the normal range, subjects with total T3 (or FT3) and FT4 within the normal range can also be enrolled;
* Subjects of childbearing potential must use an appropriate method of contraception during the study period and within 120 days after the end of the study, have a negative serum pregnancy test within 7 days prior to study enrollment, and must be non-lactating subjects ；

Exclusion Criteria:

* Suffered from other malignant tumors within 5 years before the start of treatment in this study;
* Pathologically suggested patients with abnormally increased AFP OR MSI-H ；
* Grade ≥1 unresolved toxicities (according to the most recent version of the National Cancer Institute \[NCI\] Common Terminology Criteria for Adverse Events \[CTCAE\]) due to any prior therapy, excluding alopecia and fatigue; neurotoxicity was Recovery to ≤ grade 1 or baseline before the group;
* Subjects with any severe and/or uncontrolled disease ；
* Poorly controlled diabetes (fasting blood glucose \[FBG\] \> 10 mmol/L) ；
* Received major surgical treatment, incisional biopsy, or significant traumatic injury within 28 days prior to the start of study treatment; or had a long-term unhealed wound or fracture；
* Serious arterial/venous thrombotic event within 6 months prior to initiation of study treatment ；
* Previously received drug therapy against PD-1, PD-L1 and other related immune checkpoints ；
* Participating in or participating in other clinical investigators within 4 weeks prior to the start of the study ；
* Allergic to the active ingredients or excipients of the study drug ；
* Unsuitable for the study or other chemotherapy determined by investigator.