Cancer of Unknown Primary: Diagnosis and Treatment

Cancer of unknown primary (CUP) is a heterogenous group of cancers for which the anatomical site of origin is unidentifiable on the basis of standard evaluation and imaging. CUPs account for 2-5% of all malignancies and are characterized by early metastatic dissemination, aggressive clinical course, and poor response to palliative chemotherapy. It is important to identify favorable-risk CUP patients (10-20%), as they harbor chemo-sensitive and potentially curable tumors, and may require long-term disease control. Empirical combination chemotherapy has traditionally been the standard first-line therapy for most patients (80-90%), who do not belong to favorable-risk subsets; however, this approach has only modest benefits, with a median overall survival of < 1 year. Evidence supporting the clinical use of molecular tissue of origin (TOO) tests is still lacking. Two recent randomized clinical trials failed to show the benefit of TOO-based site-specific therapy over empirical chemotherapy. In an era of precision medicine, the use of comprehensive molecular profiling will provide opportunities to identify patient subsets who are susceptible to targeted therapies and immunotherapies.