PD-1 Inhibitor and Nab-paclitaxel and Bevacizumab in CUP

Inclusion Criteria: 1. The histopathologically confirmed metastasis is adenocarcinoma, squamous cell carcinoma, poorly differentiated carcinoma, poorly differentiated malignant tumor or neuroendocrine carcinoma; 2. Patients whose primary lesions cannot be found after standard evaluation prior to treatment: detailed history, physical examination, blood test, chest and pelvic CT, PET/CT (optional), endoscopy of symptomatic sites, and pathological examination; 3. Measurable lesions (RECIST 1.1 criteria); 4. Patients who have progressed after receiving first-line treatment for Carcinoma of Unknown Primary. For example, those who have received paclitaxel or docetaxel in the first-line treatment and progressed more than three months after the end of last treatment; 5. ECOG of 0-2; 6. Life expectancy\>3 months; 7. Within 7 days (including 7 days) before screening, the laboratory test data requirements: neutrophil count ≥1.5×10\^9/L, platelet count ≥90×10\^9/L, hemoglobin ≥90g/L (No blood transfusion in 14 days), serum total bilirubin ≤1.25 times the upper limit of normal (ULN); ALT and AST≤2.5 x ULN (patients with liver metastases ≤5x ULN); serum creatinine ≤1.25 x ULN Exclusion Criteria: 1. Patients who have previously been treated with albumin paclitaxel or bevacizumab or PD-1 monoclonal antibody; 2. Received any experimental drugs or anti-tumor drugs within 4 weeks prior to enrollment; 3. A history of other tumors in the past 5 years, except for cervix or basal cell carcinoma of the skin that has been cured; 4. Symptomatic brain or meningeal metastases (unless the patient receives treatment for\> 6 months, the imaging results are negative within 4 weeks before entering the study, and the clinical symptoms related to the tumor are stable at the time of entering the study). NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.