Cytology of desmoplastic small round cell tumor

Desmoplastic small round cell tumor (DSRCT) is a high-grade malignant tumor that has a predilection for adolescent males and usually affects the abdominal cavity. The cytology literature regarding DSRCT, including aspirates and ascitic fluid, is limited. To the authors' knowledge, findings in ThinPrep slides have not been described previously.

Seven cytologic specimens from five patients with histologically confirmed DSRCT were reviewed. Five specimens were fine-needle aspiration biopsies (FNABs), (liver, flank soft tissue, abdomen, and two resected colons [pericolic]) and two specimens were ascitic fluid. Cytologic features were studied in ThinPrep slides and direct smears, which included hematoxylin and eosin, Papanicolaou, and Quik-Dip stains.

All specimens showed moderate to high cellularity. The tumor cells were arranged singly and in clusters. The cells demonstrated high nuclear/cytoplasmic ratios, granular chromatin reminiscent of small cell carcinoma, usually inconspicuous nucleoli, smooth to irregular nuclear membranes, and frequent nuclear molding. The cytoplasm was scant to moderate, pale blue, and occasionally vacuolated. Pseudorosettes were observed in six specimens. One ThinPrep slide and the direct smears contained cells with perinuclear, cytoplasmic densities. Stromal fragments were present in the direct smears but were uncommon in ThinPrep. Three specimens were diagnosed as being consistent with DSRCT. Two specimens were diagnosed as malignant small cell tumor. Molecular studies performed on histologic material in four cases confirmed the presence of the diagnostic translocation, t(11;22)(p13;q12).

DSRCT may be diagnosed accurately in cytology specimens. Characteristic cytologic features include granular chromatin, smooth to irregular nuclear membranes, nuclear molding, cytoplasmic vacuoles, pseudorosettes, and metachromatic stroma. Cytoplasmic densities may be observed in direct smears and ThinPrep slides.