The goal of this clinical trial is to evaluate the efficacy and safety of radiotherapy combined with chemotherapy and anti-PD-1 immunotherapy followed by surgery for the primary and metastatic lesions in patients with limited metastatic gastric or gastroesophageal junction adenocarcinoma. The main questions it aims to answer are: 1) If the multimodal treatment which includes anti-PD-1 immunotherapy and local therapies will improve the survival of this group of patients. 2) If the multimodal treatment which includes anti-PD-1 immunotherapy and local therapies can be performed safely in this group of patients.
Participants will receive short course hypofractionated radiotherapy (HFRT) for the primary lesion, HFRT or stereotactic body radiotherapy (SBRT) for metastatic lesions, combined with systemic chemotherapy and anti-PD-1 immunotherapy. For patients with HER2-positive cancer (defined as IHC 3+ or 2+/ISH+), trastuzumab is used along with chemotherapy and anti-PD-1 antibody. Then, surgical resections of primary and metastatic lesions are performed as much as possible. For patients who need a widely invasive surgical approach or are inoperable, local ablative therapies such as radiofrequency ablation (RFA) and microwave ablation (MVA) can be alternatives. For patients undergoing surgical resections, postoperative treatment includes chemotherapy, which is determined by the researcher, and PD-1 antibody, which will be maintained until one year after surgery.
Histopathologically confirmed adenocarcinoma of stomach (G) or gastroesophageal junction (GEJ) (excluding Siewert type I).
Limited metastatic status of disease.
At least one evaluable lesion in CT/MRI according to RESIST 1.1 is required.
The status of HER2 is clear.
Patients who have previously received surgery, chemotherapy, radiotherapy or immunotherapy for gastric cancer.
Patients have a history of cancer in the five years before enrollment except for squamous or basal cell carcinoma of the skin that was effectively treated and superficial bladder cancer, cervical carcinoma in situ and breast cancer in situ that was treated by operation.
Pregnant or lactating females or females planning to become pregnant or lactating. Women of childbearing age with a positive pregnancy test or without a pregnancy test in the baseline period. Menopausal women must have stopped menstruating for at least 12 months before being considered to have no chance of pregnancy.
Patients who had sexual activity (with the possibility of childbirth) and were unwilling to use contraception during the study period.