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.
Single group
Radiotherapy targeted to the primary lesion
Radiation5 to 7 fractions of short course hypofractionated radiotherapy (HFRT) targeted to the primary lesion.
Radiotherapy targeted to the metastatic lesions
RadiationHypofractionated radiotherapy (HFRT) or stereotactic body radiotherapy (SBRT) targeted to metastatic lesions. The target dose will be adjusted based on the lesion's site and diameter and organs at risk, with high-dose irradiation of 4-8 fractions. All metastatic lesions should be irradiated as much as possible, and partial lesion irradiation should be allowed when technically impractical.
Anti-PD-1 monoclonal antibody
Biological/VaccineThe anti-PD-1 mAb is used on day 1 along with each cycle of chemotherapy. There are no restrictions on the choice of anti-PD-1 mAb. Patients can choose commonly used accessible monoclonal antibodies based on their personal preferences and financial status. The commonly used anti-PD-1 mAb usages are as follows: Nivolumab/Toripalimab 240mg solution intravenously once daily, Q2W. OR Nivolumab/Toripalimab 360mg solution intravenously once daily, Q3W; OR Pembrolizumab/Tislelizumab/Sintilimab/Camrelizumab, 200mg solution intravenously once daily, Q3W.
Trastuzumab
Biological/VaccineFor patients with HER2-positive cancer (defined as IHC 3+ or 2+/ISH+), trastuzumab is used along with chemotherapy and anti-PD-1 antibody. The 3-weekly schedule of trastuzumab starts with a loading dose of trastuzumab of 8 mg/kg, followed by 6 mg/kg trastuzumab every 21 days.
Chemotherapy
DrugThe investigator's choice of chemotherapy regimens included SOX, XELOX or FOLFOX. Their usages are as follows: SOX: S-1 twice a day, days 1-14, the dose of S-1 is accorded to body-surface area (BSA): patients with a BSA of less than 1.25 m2 receive 80 mg daily; those with a BSA of 1.25 m2 or more but less than 1.5 m2 receive 100 mg daily; and those with a BSA of 1.5 m2 or more receive 120 mg daily; and oxaliplatin 130 mg/m2, day 1, every 3 weeks; XELOX: Capecitabine 1000 mg/m2 twice a day, days 1-14 and oxaliplatin 130 mg/m2, day 1, every 3 weeks; FOLFOX: Leucovorin 400 mg/m2, day 1, fluorouracil 400 mg/m2, day 1 and 1200 mg/m2, days 1-2, and oxaliplatin 85 mg/m2, day 1, every 2 weeks.
R0 total/subtotal gastrectomy with D2 lymphadenectomy
Procedure/SurgeryFor patients with a good response to preoperative treatment, surgical resection of primary and metastatic lesions is recommended. For primary lesions, gastrectomy with standard D2 lymphadenectomy is commonly used. The type of gastrectomy performed depends on the location and extent of the primary lesion. For GEJ or upper-third tumors, a 3 cm esophageal margin is recommended, and a total gastrectomy or esophagogastrectomy is performed. For middle-third tumors, the gastric margin is recommended to be more than 5 cm, and total gastrectomy is performed. For lower-third tumors, a 2 cm duodenal margin is recommended, and subtotal or total gastrectomy is performed. Billroth I or Roux-en-Y gastrojejunostomy is performed for distal gastrectomy patients. Roux-en-Y esophagojejunostomy is performed for patients receiving total gastrectomy.
Metastasectomy
Procedure/SurgeryFor patients with a good response to preoperative treatment, surgical resection of primary and metastatic lesions is recommended. For metastatic lesions, the surgical procedure and resection range are determined by the surgeon.
Local ablative therapies
Procedure/SurgeryLocal ablative therapies such as radiofrequency ablation (RFA) and microwave ablation (MVA) achieve high rates of complete tumor eradication of small metastases, and can be seen as alternatives if a widely invasive surgical approach is required or patient is inoperable.
Overall survival (OS)
The time from enrollment to death due to any reason.
No evidence of disease (NED) rate
Rate of no evidence of disease for one year
Objective response rate (ORR)
Proportion of patients with complete response (CR) or partial response (PR) to preoperative multimodal therapy. ORR will be evaluated using RESIST1.1 by CT/MRI of the chest, abdomen, and pelvis.
Progression-free survival (PFS)
The time from enrollment to disease progression or death from any cause.
Toxicities
Number of participants with treatment-related adverse events (TrAEs) reported between the first dose and 28 days after the last dose of study therapy as assessed by the National Cancer Institute Common Terminology Criteria for Adverse Events (NCI-CTCAE), version 5.0.
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