A Randomized, Multicenter Phase II Basket Study of Hypofractionated Radiotherapy/Stereotactic Body Radiotherapy Followed by Immunotherapy-Based Systemic Therapy +/- L. Rhamnosus M9 for the First-Line Treatment of Advanced Digestive System Malignancies.

Inclusion Criteria: * histopathologically confirmed diagnosis of malignant tumors of the gastrointestinal tract (including Her-2 negative adenocarcinoma of the gastroesophageal junction/gastric adenocarcinoma, hepatocellular carcinoma, malignant tumors of the biliary system, colorectal cancer); * advanced patients evaluated as initially non-operable resectable who have not received any antitumor therapy; * have at least one measurable or evaluable lesion according to RECIST v1.1 criteria in addition to the primary lesion, with non-operable resectable lymph node metastases to the liver, lung, bone, pelvis, retroperitoneum and/or superficial sites (except for brain metastases), as evaluated by discussion in the framework of the MDT * age 18-75 years; * ECOG score of 0-1; * be able to accept the treatment regimen during the study; * sign a written informed consent. Exclusion Criteria: * a history of uncontrolled epilepsy, central nervous system disease, or psychiatric disorder of clinical severity that, in the judgment of the investigator, may preclude the signing of an informed consent form or interfere with the patient's adherence to oral medication; * prior immunotherapy for any indication or a history of severe hypersensitivity reactions to other monoclonal antibodies; * clinically significant (i.e., active) cardiac disease, such as symptomatic coronary artery disease, New York Heart Association (NYHA) class II or worse congestive heart failure or severe arrhythmias requiring pharmacologic intervention, or history of myocardial infarction within the last 12 months; * organ transplantation requiring immunosuppressive therapy; * a history of other malignant disease within the last five years; * persons with severe uncontrolled recurrent infections, or other severe uncontrolled concomitant diseases; * Subjects whose baseline blood routine and biochemical indexes do not meet the following criteria: hemoglobin ≥80g/L; absolute neutrophil count (ANC) ≥1.5×10\^9/L; platelets ≥100×10\^9/L; ALT, AST ≤2.5 times the upper limit of normal; ALP ≤2.5 times the upper limit of normal; serum total bilirubin \<1.5 times the upper limit of normal; serum creatinine \<1 times the upper limit of normal; and serum creatinine \<1 times the upper limit of normal. times the upper limit of normal; * the patient currently has active gastrointestinal diseases such as active gastric and duodenal ulcers, ulcerative colitis, or active bleeding from unresected tumors, or other conditions that may cause gastrointestinal bleeding or perforation as determined by the investigator; * persons with active bleeding or bleeding tendencies; * women who are pregnant or breastfeeding; * allergy to any of the study drug ingredients.