Cancer of unknown primary site(CUP)is not a rare entity for 3-5% of all malignant neoplasms. CUPis diagnosed with metastatic lesion so they are all in the advanced stage. The diagnosis is made by biopsy. Patients with CUP need to have a physical examination, basic blood examination and appropriate diagnostic imaging. Those are valuable for final diagnosis of primary site determination. Systemic chemotherapy is applied in many cases, but the standard therapeutic strategy has not yet been determined.