Desmoplastic Small Round Cell Tumor : Desmin

Desmoplastic small round cell tumor (DSRCT) is a rare highly aggressive tumor of adolescent and young adults with a strong male predominance. It usually involves abdominal or pelvic peritoneum. The tumor is large and multinodular with a firm, gray-white cut surface and areas of hemorrhage, necrosis and cystic change. It is composed of undifferentiated small blue cells arranged in sharply demarcated nests in a background of vascular desmoplastic stroma. Rare cases show significant nuclear atypia and single filing pattern (reminiscent of lobular breast carcinoma) or Homer Wright-like rosettes. Most cases co-express epithelial (cytokeratin AE1/AE3, EMA), mesenchymal (vimentin, desmin - paranuclear dot-like positivity), and neural markers (NSE). WT1 is positive (antibody to carboxy terminus; nuclear expression). DSRCT shows chromosomal translocation t(11:22) (p13; q12) involving the EWSR1 gene (22q12) and WT1 gene (11p13). The translocation results in the expression of a chimeric EWSR1-WT1 protein that acts as a powerful mitogen and permits tumor growth. The EWSR1-WT1 fusion can be detected by RT-PCR or FISH. The differential diagnosis included other small round blue cell tumors. The treatment consists of a combination of extensive debulking procedure, intraperitoneal/systemic chemotherapy, radiotherapy with or without stem cell transplantation. The prognosis is dismal with a 5-yr survival rate of less than 15%.