Desmoplastic small round cell tumor: diagnosis by fine-needle aspiration cytology

Desmoplastic small round cell tumor (DSRCT) is a distinctive clinicopathologic entity with an aggressive clinical course that typically involves the abdominal and/or pelvic peritoneum of young males. A population of small round blue cells and a fibroesclerotic stroma are the usual morphologic features. This tumor is characterized by a typical polyphenotypic profile with expression of epithelial, mesenchymal and neural markers. Cytogenetically, this tumor presents a unique abnormality - t(11;22)(p13;q12).

A 29-year-old male without significant medical history was admitted to our institution with gastrointestinal symptomatology. The physical examination and medical imaging studies revealed an extensive soft tissue mass filling the entire peritoneal cavity/pelvis. A fine-needle aspiration (FNA) of the abdominal mass was performed. The FNA smears revealed fragments of collagenous desmoplastic stroma and clusters of loosely cohesive small round cells that showed positivity for epithelial and myogenic markers. Cytogenetic analysis demonstrated rearrangement of the genes EWSR1 and WT1, resulting from the t(11;22)(p13;q12).

DSRCT is an uncommon neoplasm that shares clinical and cytomorphologic features with other small round cell tumors. Therefore, a primary definitive diagnosis based on cytology specimens may be difficult but plausible and can be aided by a typical clinical presentation and ancillary immunocytochemical/cytogenetic studies.