A Phase II/III Study of F520 Combined With Paclitaxel Plus Carboplatin in the Treatment of Cancer of Unknown Primary (CUP)

Inclusion Criteria: * Age 18-75 years (inclusive), any gender Histopathologically confirmed adenocarcinoma, squamous cell carcinoma, poorly differentiated carcinoma, or undifferentiated carcinoma of metastatic lesions Diagnosis of CUP after standard evaluation (see Appendix 4) No prior systemic therapy for CUP At least one measurable lesion per RECIST 1.1 criteria Eastern Cooperative Oncology Group (ECOG) performance status score of 0-1 Investigator-assessed life expectancy ≥3 months Adequate organ function as follows (no blood products or hematopoietic growth factors within 14 days before first dose): Hematology: ANC ≥1.5×10⁹/L; Platelet count ≥90×10⁹/L; Hemoglobin (Hb) ≥90 g/L Liver Function: AST, ALT ≤2.5×ULN; Total bilirubin (TBIL) ≤1.5×ULN; If liver metastases present: AST and ALT ≤5×ULN, TBIL ≤3×ULN Renal Function: Serum creatinine (Cr) ≤1.25×ULN Coagulation: INR ≤1.5×ULN and APTT ≤1.5×ULN Understanding of study procedures and content, and voluntary signed informed consent Exclusion Criteria: * CUP patients who, in the investigator's judgment, are candidates for local curative treatment Histopathologically confirmed neuroendocrine carcinoma or germ cell tumor of metastatic lesions Prior genetic testing (including but not limited to NGS) showing NTRK fusion-positive, ALK fusion-positive, EGFR sensitizing mutations, BRAF mutations suitable for molecular targeted therapy, or MSI-H/dMMR Genetic testing (including but not limited to 90-gene assay) suggesting possible co…