MRI DWI None-Gaussian Model Predicting Early Response to Immunotherapy in Digestive System Malignancies: a Prospective Observational Study

Inclusion Criteria: * age ≥ 18 years, ECOG 0-1, expected survival ≥3 months; * pathologically confirmed digestive system adenocarcinoma, including but not restricted to gastric adenocarcinoma, colorectal cancer, pancreatic adenocarcinoma et al; * pathologically confirmed PD-L1 expression, or MMR-deficient (dMMR)/microsatellite instability (MSI-H) or high tumor mutation burden (TMB-H) or other indication for immunotherapy; * at least one target lesion, if there is no target lesion the thickness of cavity viscera lesion should exceed 1cm; * patients will receive single agent PD-1/PD-L1 inhibitor, or combined immunotherapy such as: lenvatinib, enrotinib or herceptin; * screening laboratory values must meet the following criteria: hemoglobin ≥ 9.0 g/dL; neutrophils ≥ 1500 cells/ μL; platelets ≥ 100 x 10\^3/ μL; total bilirubin ≤ 2.0 x upper limit of normal (ULN); aspartic transaminase (AST) and alanine transaminase (ALT) ≤ 2.5 x ULN without, and ≤ 5 x ULN with hepatic metastasis; serum creatinine ≤1.5 x ULN, and serum creatinine rate \>50μmol/L; activated partial thromboplastin time (APTT)、international normalized ratio (INR), prothrombin lime (PT)≤1.5×ULN; * echocardiography: left ventricular ejection fraction≥50% * volunteer participate, signed written informed consent form. Exclusion Criteria: * claustrophobia or other contraindication for MRI testing; * received prior anti-PD-1/PD-L1 or other immune checkpoint inhibitors; * combined immunotherapy contains chemotherapy agent; * contain other histology component except adenocarcinoma； * hypersensitivity after other monoclonal antibody infusion； * coexist other malignancy in last five years; * active autoimmune disease, or who received systemic treatment with corticosteroids (\> 10 mg daily prednisone equivalent) or other immunosuppressive medications within 2 weeks of first dose; * Cavity effusion (pleural effusion, ascites, pericardial effusion, etc.) are not well controlled, and need locally treatment or repeated drainage; * obvious bleeding tendency or had CTCAE≥3 grade； * subjects are eligible with clinically controlled and stable neurologic function ≥ 4 weeks, which is no evidence of CNS disease progression; subjects with spinal cord compression and cancerous meningitis are not eligible； * vaccination within 28 days of the first administration of trial treatment.