When desmoplastic small round cell tumor (DSRCT) is present in serous fluid, the cytomorphology can be diverse and can mimic metastatic carcinomas and thus present a diagnostic challenge. The aim of this study was to evaluate the cytomorphologic and immunocytochemical features of this rare tumor in serous effusion specimens.
Demographic, clinical, radiologic, and pathologic information from patients who had a DSRCT diagnosis on body fluid specimens was collected and cytologic slides were reviewed.
Nine specimens were identified (5 pleural fluid and 4 ascitic fluid specimens) from 8 patients (5 male and 3 female). The mean patient age at diagnosis was 26 years. The most common symptoms were abdominal distension and pain, with 5 patients having abdominal masses. Other findings included peritoneal carcinomatosis, liver masses, ascites, and pleural nodules. The predominant cytomorphology was loose cellular clusters, followed by tight clusters of small cells with scant occasional vacuolated cytoplasm and a sphere-like pattern.
Serous fluid may be the first available specimen to diagnose DSRCT. In young patients with no history of malignancy and radiologic finding of peritoneal implants, DSRCT should be considered a possibility in the differential diagnosis, and sensitive markers should be used for accurate diagnosis.

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