Effusion cytology: Keeping researchers and journals in business for the past 20 years-and it is not over yet

Malignant cells, both mesothelioma and metastases, can be difficult to distinguish from reactive benign mesothelial cells. Careful attention must be paid to the morphology of the questionable cells as well as any background inflammation and pertinent clinical history. Various diagnostic adjuncts have been investigated, particularly immunocytochemistry, but with no firm consensus regarding an optimal approach to resolving difficult cases. This review examines the morphology, immunocytochemistry and future directions of effusion cytology.