Desmoplastic small round-cell tumor: A case report on the large cell variant with immunohistochemical, ultrastructural, and molecular genetic analysis

A case of large cell desmoplastic small round-cell tumor (DSRCT) is described. The tumor arose in a 23-year-old man who was found to have a 14-cm-diameter omental mass during ultrasonographic examination. The patient died 10 months after surgery. Histologically, the tumor was composed of predominantly large epithelioid cells with foci of anaplasia mimicking metastatic carcinoma. Immunohistochemically, the tumor cells stained with anti-cytokeratin. EMA. desmin, and NSE antisera. Electron microscopy showed secretory lumina, desmosomes, cell processes with microtubules and electron-dense granules, and focal whorls of intermediate filaments. Reverse transcriptase-polymerase chain reaction performed on paraffin block-retrieved tissue demonstrated the EWS/WT-1 fusion transcript characteristic of the t(11;22)(p13;q12). This case illustrates a less common histological pattern of DSRCT, i.e.. diffuse large cells, thus supporting the view that this tumor presents a wider morphological spectrum than that previously recognized.