Occult Lymph Node Metastasis from Desmoplastic Small Round Cell Tumor Diagnosed by Fine Needle Aspiration Cytology

BACKGROUND Desmoplastic small round cell tumor (DSRCT) is a rare but well-defined neoplasm generally forming in the abdominal or pelvic cavity of young males and has distinct clinical, immunohistochemical and molecular features. Cytologic features of DSRCT have been described on fine needle aspiration of primary tumors. An occult lymph node metastasis of DSRCT diagnosed through the cytologic features, a basic immunocytochemical panel and DNA ploidy evaluation on cytospins obtained by fine needle aspiration is reported. CASE Aspiration cytology was performed on an inguinal lymph node from a 20-year-old male. A Diff-Quik-stained smear showed mature lymphocytes and groups of undifferentiated, small cells with scanty cytoplasm, dense and coarse chromatin, and small nucleoli. Basic immunocytochemical stains showed negativity for leukocyte-common antigen and neuron-specific enolase and positivity for cytokeratin cocktail (Cam 5.2), vimentin and desmin, the last with characteristic paranuclear dotlike positivity. DNA ploidy evaluation showed an aneuploid histogram with a low 5c exceeding rate. CONCLUSION Cytologic and immunocytochemical features suggest the diagnosis of DSRCT on fine needle aspiration cytology samples even in cases of a metastatic, unknown primary tumor. Because of the tumor's aggressiveness, a rapid and accurate diagnosis is required.