RESIDENT CASE STUDIES

Week 3 May 5 - May 9, 2003: Case 4   

Table of Contents | List of Diagnoses | Case 1 | Case 2 | Case 3 | Case 4 

Discussion: Desmoplastic Small Round Cell Tumor
Desmoplastic small round cell tumor (DSRCT) is a relatively uncommon tumor with an aggressive clinical course, and typically involves the abdominal or pelvic peritoneum. It may arise rarely in extraabdominal sites, such as thoracic region, paratesticular region, ovary, parotid gland, hand and central nervous system. The common age range is 15-35 years, with a male to female ratio of 4:1. Clinically patients present with abdominal symptoms (pain, distention, ascites), large abdominal/pelvic mass without an identifiable visceral site of origin, intestinal or urethral obstruction and impotence. 

Microscopically, sharply demarcated nests of relatively uniform small round/oval cells with hyperchromatic nuclei are embedded in a hypervascular desmoplastic stroma. Rhabdoid-like cells with paranuclear intracytoplasmic hyaline inclusions are relatively common. Sometimes these tumor cells can be arranged in cords and can mimic lobular carcinoma of the breast. The cell of origin is not clear. Immunohistochemically, these tumor cells are multiphenotypic and stain with epithelial (cytokeratin-except 5,6 and 20), mesenchymal (vimentin, desmin-perinuclear dot-like pattern ) and neural markers (85% neuron-specific enolase and 49% leu-7). One-third of the DSRCT are positive for CD99.  CA-125 may be expressed in some DSRCT. 

The common cytogenetic abnormality is t(11;22) (p13;q12). Molecular studies are helpful in identifying  EWS-WT1 fusion transcript. New polyclonal  anti-WT1 antibodies have been developed to detect WT1 protein in DSRCT, which facilitates the diagnosis, if tissue for molecular studies is not available. Complete surgical resection is not possible in these tumors. But, debulking followed by systemic chemotherapy may improve survival, if not the prognosis.

 Differential diagnosis:

Rhabdomyosarcoma: Small round blue cells with strap cells or rhabdoid cells are seen . Rhabdoid cells with eosinophilic cytoplasmic bellies and cross striations are diagnostic. These cells are positive for Myo-D1 and desmin. 

Ewing’s sarcoma: Small round blue cell tumors with minimal surrounding stroma. Can be skeletal or extraskeletal. Males and females are equally affected. The tumor cells are positive for CD99, variably positive for Ck and vimentin and negative for desmin. 

Neuroblastoma: Commonly seen before 5 years. Histologically, Homer-Wright rosettes with fibrillary background. Immunohistochemical stains are positive for synaptophysin, chromogranin and neuron-specific enolase. Mature or immature ganglion cells may be seen in differentiated tumors. Calcifications are common. 

Malignant mesothelioma: Usually seen in older people with history of asbestos. A panel of immunohistochemical stains are helpful, as there is no specific marker for mesothelioma. The tumor cells are positive for cytokeratin (5/6), vimentin, calretinin, EMA (membranous) and negative for MOC31, B72.3, Leu-1, and CEA.

References:

Fletcher, CBM, Unni, KK, Mertens, F (Eds.): World Health Organization Classification of Tumors. Pathology and Genetics of Tumors, Soft Tissue and Bone. IARC Press: Lyon 2002.

Weiss, SW, Goldblum, JR, Enzinger, FM (2001). Enzinger and Weiss's Soft Tissue Tumors (46th ed.). Philadelphia, PA: Mosby.