Phase I/II Clinical Study of Decitabine Combined With TQB2450 Injection or Decitabine + Anlotinib Combined With TQB2450 Injection in the Treatment of PD-1 Monoclonal Antibody-resistant Digestive System Tumors

Inclusion Criteria: * Voluntary participation and written informed consent; * Age: 18-70 years old; * No gender limitation; * Digestive system malignant tumor diagnosed by pathology; * Previously received PD-1 monoclonal antibody Or the combination therapy fails; * There is at least one measurable lesion (according to the RECIST1.1 standard) or an unmeasurable lesion that can be evaluated, and the imaging diagnosis is ≤21 days from the selection time； * The expected survival period is ≥3 months; * General physical status (ECOG) 0-1; * Sufficient bone marrow hematopoietic function (within 7 days); normal liver and kidney function (within 14 days)； * Heart, lung, kidney, and liver functions are generally normal. Exclusion Criteria: * People who are currently receiving other effective treatments; * Patients who have been treated with anti-vascular TKI drugs in the past; * Patients who have participated in other clinical trials within 4 weeks before enrollment; * Allergic to study drugs; * Those without measurable tumor lesions, such as body cavity effusion or diffuse infiltration of organs; * Those with measurable lesions that have received radiotherapy. * Patients with other primary malignant tumors other than digestive system tumors at the same time, except for early solid tumors that have been cured for more than 1 year; * Clinically significant cardiovascular diseases, such as heart failure (NYHAIII-IV), are not controlled A history of coronary heart disease, cardiomyopathy, arrhythmia, uncontrolled hypertension or myocardial infarction within the past 1 year; * Neurological or mental disorders that affect cognitive ability, including central nervous system metastasis; * Existed within 14 days before enrollment Active severe clinical infections (\>grade 2 NCI-CTCAE version 5.0), including active tuberculosis; * Known or self-reported HIV infection or active hepatitis B or C; * Uncontrolled Systemic diseases, such as poorly controlled diabetes; * A history of interstitial lung disease, such as interstitial pneumonia, pulmonary fibrosis, or evidence of interstitial lung disease on baseline chest X-ray/CT; * Keratitis , Ulcerative keratitis or severe dry eye; * Known hypersensitivity or allergic reaction to any component of the study drug; * Pregnancy (determined by serum β-chorionic gonadotropin test) or breast-feeding.