Cytologic features of intraabdominal desmoplastic small round cell tumor. A case report.

Intraabdominal desmoplastic small round cell tumor (IAD-SRCT) is a highly aggressive, malignant neoplasm that affects predominantly young adult males. This report describes the fine needle aspiration and ascitic fluid cytology findings in a 15-year-old male with IAD-SRCT. The tumor cells consisted of small, round to oval cells with a scant amount of basophilic cytoplasm. No cytologic evidence of cellular differentiation was identified. The similarities of cytologic features with other small round cell tumors in the pediatric age group may lead to differential diagnostic difficulties that require the application of ancillary diagnostic methods, such as immunohistochemistry, electron microscopy and cytogenetic techniques. In this case, immunohistochemical stains were positive for cytokeratin, desmin and neuron-specific enolase. Flow cytometry revealed a tetraploid DNA stemline and proliferation index of 21% (S + G2M). Ultrastructural examination revealed undifferentiated small cells with large, perinuclear whorls of intermediate filaments. Cytogenetic studies showed a grossly abnormal karyotype with a t(11;17)(p13;q11.2) translocation and a near-tetraploid modal chromosome number. This karyotype differed from those in previous cases in that it lacked a 22q12-13 fusion partner but provided further evidence for involvement of the 11p13 region in the pathogenesis of this unusual tumor.