Desmoplastic Small Round Cell Tumor of the Uterus: A Report of Molecularly Confirmed Case with EWSR1-WT1 Fusion

EWSR1::WT1 Fusions in Neoplasms Other Than Conventional Desmoplastic Small Round Cell Tumor: Three Tumors Occurring Outside the Female Genital Tract

Desmoplastic small round cell tumor (DSRCT) is a high-grade, primitive round cell sarcoma classically associated with prominent desmoplastic stroma, coexpression of keratin and desmin, and a characteristic EWSR1::WT1 gene fusion. DSRCT typically arises in the abdominopelvic cavity of young males with diffuse peritoneal spread and poor overall survival. Although originally considered to be pathognomonic for DSRCT, EWSR1::WT1 gene fusions have recently been detected in rare tumors lacking the characteristic morphologic and immunohistochemical features of DSRCT. Here, we report 3 additional cases of neoplasms other than conventional DSCRCT with EWSR1::WT1 gene fusions that occurred outside the female genital tract. Two occurred in the abdominopelvic cavities of a 27-year-old man and a 12-year-old girl, whereas the third arose in the axillary soft tissue of an 85-year-old man. All cases lacked prominent desmoplastic stroma and were instead solid and cystic with peripheral fibrous pseudocapsules and occasional intervening fibrous septa. Necrosis was either absent (1/3) or rare (2/3), and mitotic activity was low (<1 to 3 per 10 hpf). In immunohistochemical studies, there was expression of smooth muscle actin (3/3) and desmin (3/3), rare to focal reactivity for EMA (2/3), and variable expression of CK AE1/AE3 (1/3). Myogenin and MyoD1 were negative, and C-terminus-specific WT1 was positive in both cases tested (2/2). All 3 tumors followed a more indolent clinical course with 2 cases demonstrating no evidence of disease at 20 and 44 months after resection. The patient from case 3 died of other causes at 14 months with no evidence of recurrence. DNA methylation profiling showed that the 3 cases clustered with DSRCT; however, they demonstrated fewer copy number variations with 2 cases having a flat profile (0% copy number variation). Differential methylation analysis with hierarchical clustering further showed variation between the 3 cases and conventional DSRCT. Although further study is needed, our results, in addition to previous reports, suggest that EWSR1::WT1 gene fusions occur in rare and seemingly distinctive tumors other than conventional DSRCT with indolent behavior. Proper classification of these unusual soft tissue tumors with EWSR1::WT1 gene fusions requires direct correlation with tumor morphology and clinical behavior, which is essential to avoid overtreatment with aggressive chemotherapy.

Giant desmoplastic small round cell tumor of the abdomen: A case report

BACKGROUND

Desmoplastic small round cell tumor (DSRCT) is a rare, aggressive, mesenchymal malignancy of a separate clinicopathological entity. It has a predilection for young men, with no evidence of any ethnic predilection. The current diagnostic gold standard for DSRCT includes histopathologic, immunohistochemical, and cytogenetic studies in order to confirm the variable phenotypic expression and characteristic chromosomal translocation.

CASE SUMMARY

A 65-year-old man presented with a sensation of an abdominal mass and a presentation of an incomplete bowel obstruction. Initial lab tests were in the normal range except for carbohydrate antigen. Contrast-enhanced CT showed that a large, mass-confounding density was occupied in the omentum majus area of the middle and lower abdominal wall. A 3D reconstruction of the images was performed to clarify the relationship between the tumor and the colon and was confirmed by a colonoscopy. After surgery, immunohistochemistry and fluorescence in situ hybridization (FISH) revealed EWSR1-WT1 gene rearrangement at 22q12, confirming the diagnosis of desmoplastic small round cell tumor.

CONCLUSION

Being different from the predilection of DSRCT for young men, the patient in our case is a 65-year-old man with a huge mass involving the transverse colon and the bladder.