Accuracy and reproducibility of pleural effusion cytology.

In order to evaluate the accuracy and the reproducibility of cytological diagnosis based on morphological criteria alone, nine cytopathologists from seven different institutions, in two rounds, blindly examined 45 smears of mesotheliomas (17), metastases (14 ) and benign effusions (14). All the diagnoses had been confirmed by clinical follow-up and eventually by autopsy. Diagnostic accuracy (comparison with the standard), interobserver and intraobserver agreement in the distinction of benign vs malignant cases, the differentiation of primary from metastatic malignancies, and the evaluation of experts versus non-experts (residents) have been evaluated employing different statistical approaches. Accuracy and reproducibility resulted satisfactory in the distinction of benign from malignant smears (overall K=0.514), but markedly decreased when the differential diagnosis of malignant mesotheliomas from metastases was considered (overall K = 0.343). Cytology is a useful tool in the identification of malignancies; when the distinction of primary from metastatic tumours is addressed, morphological criteria alone are not sufficient for a definite diagnosis and the use of cell blocks, immunohistochemistry (ICC) and molecular ancillary techniques are recommended.