Diagnosis of mesothelioma by cytology using Japanese criteria

Mesotheliomas produce body cavity effusion in about 70% of cases. Their cytologic diagnosis is hindered by the existence of a wide range of sensitivities, (according to the guidelines for pathologic diagnosis of malignant mesothelioma) and by the absence of a key histologic diagnostic feature, invasion of tumor cells into preexisting tissue. Early in the incidence of mesothelioma, there is just effusion, without pleural thickening, and in some cases mesothelioma cells appear in effusions temporarily, not permanently. Therefore, correct diagnosis requires effusion-sampling at the right time. The characteristic cell-features of epithelioid mesothelioma revealed by effusion cytology include: (1) cell clusters (ball-like structures, papillary structure, window-formation, cell-to-cell engulfment, and type 2 collagenous stroma), (2) round or oval nucleus with one or two prominent nucleoli, (3) multinucleated cells, (4) thick basophilic cytoplasm, (5) blurring of the cell contour, and (6) hump-like cellular processes (following the general rule for clinical and pathological record of lung cancer of the Japan Lung Cancer Society). Provided some critical criteria are met—such as a history of asbestos exposure, pleural thickening, high content of hyaluronic acid in effusions—a definitive diagnosis of mesothelioma may be possible by effusion cytology alone.