Cytological identification of metastatic epithelial nephroblastoma in pleural fluid: report of a case and review of literature.

Nephroblastoma (Wilms' tumor) is the most common childhood renal tumor and usually presents with a histology and cytology consisting of blastemal, epithelial, and stromal cells. Effusions are not uncommon and may suggest an unfavorable prognosis when containing anaplastic tumor cells. In the present case, we report the cytological appearance of a Wilms' tumor metastatic to the pleura. The effusion consisted primarily of tumor cells demonstrating epithelial differentiation. The tumor cells mostly presented as three-dimensional aggregates in an inflammatory background. Many cystic and tubular structures were identified. The tumor cells demonstrated strong CD56 and WT1 immunoreactivity. The histology of a subsequent surgical specimen reflected the features seen in cytology.