Elsevier

Human Pathology

Volume 46, Issue 1, January 2015, Pages 153-158
Human Pathology

Case study
Low-grade small round cell tumor of the cauda equina with EWSR1-WT1 fusion and indolent clinical course

https://doi.org/10.1016/j.humpath.2014.09.015Get rights and content

Summary

We report a case of a longstanding, large tumor involving spinal nerve roots of the cauda equina. The tumor showed small round cells arranged in nests and cords and immunophenotypic features of a glomus tumor, along with infrequent mitoses and a low Ki-67 labeling index, but exhibited some rosette-like structures, with focal CD99 and Neu-N expression. Subsequent molecular analysis showed the presence of an EWSR1-WT1 gene fusion by fluorescence in situ hybridization, which was confirmed by reverse- transcriptase polymerase chain reaction. To our knowledge, this is the first case reported with EWSR1-WT1 fusion in a small round blue cell tumor with smooth muscle differentiation and an indolent course.

Introduction

The t(11;22) (p13;q12) reciprocal translocation leading to production of EWSR1-WT1 fusion protein is the defining molecular alteration of desmoplastic small round cell tumor (DSRCT). DSRCT is characterized by solid sheets, nests, or cords of small round cells separated by desmoplastic stroma, and shows a distinct polyphenotypic immunohistochemical profile. It is an aggressive tumor with frequent recurrences and poor overall survival, and seen typically in the abdomen and pelvis of young males. DSRCT of the central nervous system is rare, and to date, only four cases have been reported [1], [2], [3]. Herein, we describe a case of longstanding, large tumor involving spinal nerve roots of the cauda equina; it showed morphologic and immunophenotypic features of glomus tumor, along with infrequent mitoses and a low Ki-67 labeling index, but exhibited some rosette-like structures, CD99 and focal Neu-N expression, and EWSR1-WT1 gene fusion. To our knowledge, this is the first case reported with this unusual constellation of findings.

Section snippets

Clinical summary

A 34-year-old man initially presented 10 years ago with 1-year history of intermittent back pain. His magnetic resonance imaging (MRI) of the lumbosacral region at that time showed lesions involving bilateral L4 nerve roots. The mass on the right side measured 3 × 1 cm and the left-sided tumor measured 0.7 × 0.5 cm. The lesions were isointense on T1-weighted and minimally hyperintense on T2-weighted images. Post-contrast images revealed avid enhancement. The lesion on the right expanded the

Pathologic examination

The resected specimen consisted of multiple tissue fragments measuring 6 × 5.5 cm in aggregate. Histologic sections showed a neoplasm composed predominantly of small round cells, arranged in nests and cords imparting an organoid appearance at low magnification (Fig. 2A). At higher magnification, individual nests of cells coalesced around pale, eosinophilic extracellular matrix imparting a rosette-like appearance (Fig. 2B). This central matrix was variably fibrillar resembling neuropil, focally.

Discussion

The Ewing sarcoma breakpoint region 1 (EWSR1) has been identified as a translocation partner in a wide range of clinically and pathologically diverse tumors including the Ewing family of tumors, DSRCT, clear cell sarcoma of soft parts, extraskeletal myxoid chondrosarcoma, angiomatoid fibrous histiocytoma, and myxoid liposarcoma among others [6]. More recently it has been detected in myoepithelial tumors of skin, soft tissue, and bone, clear cell sarcoma-like tumors of the gastrointestinal

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Cited by (20)

  • Mesenchymal Tumors with EWSR1 Gene Rearrangements

    2019, Surgical Pathology Clinics
    Citation Excerpt :

    Although most tumors with EWSR1-WT1 fusions represent DSRCT, this fusion is not wholly specific for it, as EWSR1-WT1 fusion transcripts have been described in 2 cases of pediatric intra-abdominal spindle cell neoplasms resembling leiomyosarcomas, but which have shown a favorable outcome.120 EWSR1-WT1 transcripts have also been found in a low-grade small round cell tumor of the cauda equina,121 which was clinically indolent and comprised nests and cords of small round cells with some rosettelike structures, infrequent mitotic figures, immunophenotypic features of smooth muscle differentiation, and focal CD99 and Neu-N expression.121 It is therefore crucial to correlate the finding of EWSR1-WT1 fusion transcripts with the clinical and pathologic findings for a correct diagnosis of DSRCT.

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There is no conflict of interest.

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