Carcinoma of unknown primary (CUP) is a biopsy-proven (mainly epithelial) malignancy for which the anatomic site of origin remains unidentified after an intensive search. CUP is one of the 10 most frequently diagnosed cancers worldwide, accounting for approximately 3–5% of all cancer cases. Most investigators do not consider lymphomas, metastatic melanomas, and metastatic sarcomas that present without a known primary tumor to be CUP because these cancers have specific stage- and histology-based treatments that can guide management. .
