Malignant pleural effusion and cancer of unknown primary site: a review of literature

Metastatic cancer of unknown primary (CUP) site refers to a heterogeneous group of cancers that are detected histologically at metastatic site but with unknown primary location despite a thorough and extensive medical evaluation (1,2). They account for 4–5% of all invasive cancers. More than half of these patients will be identified to have adenocarcinoma with multiple sites of metastasis (3). Isolated pleural effusion, as the initial presenting site for CUP is uncommon. Most of these patients portend a poor prognosis (3)