Extraskeletal Ewing's Sarcoma/Primitive Neuroectodermal Tumor of the Posterior Mediastinum with t(11;22)(q24;q12)

Abstract

Ewing's sarcoma/primitive neuroectodermal tumor family of tumors is part of a rare group of malignant neoplasms with small round-cell morphology. We describe a 24-year-old woman who presented with non-specific back pain. A chest radiograph and magnetic resonance imaging demonstrated an extraosseous, dumbbell-shaped mass of the posterior mediastinum with extension into the spinal canal. The patient underwent a left posterolateral thoracotomy and a T3-5 laminectomy with subsequent multi-agent chemotherapy. Histopathologic examination of the tumor demonstrated sheets of primitive small round malignant cells that showed no visible differentiation. Neoplastic cells were strongly immunoreactive for CD99 and vimentin and were negative for chromogranin, synaptophysin, CD31, CD34, calcitonin, desmin, low-molecular weight cytokeratins, wide-spectrum cytokeratins, leukocyte common antigen, S-100 protein, and thyroid transcription factor-1. The neoplasm was diagnosed as a Ewing's sarcoma/primitive neuroectodermal tumor, and cytogenetic studies confirmed a t(11;22)(q24;q12) chromosomal translocation and an associated trisomy of chromosome 2, supporting the histologic diagnosis. Extraskeletal Ewing's sarcoma/primitive neuroectodermal tumors are rare neoplasms that should be distinguished from other small round-cell tumors by morphology and ancillary laboratory techniques. Although rare, they need to be considered in the differential diagnosis of primary mediastinal tumors.

Multiple Ewing Sarcoma/Primitive Neuroectodermal Tumors in the Mediastinum

“…2,3,6 Wright-type rosettes can be identified in the more neurally differentiated tumors. 9 However, these histologic patterns are not specific morphologic features. Then, it is hard to differentiate the ES/PNET from similar other small round blue cell tumors such as embryonal rhabdomyosarcoma, neuroblastoma, and lymphoma by a standard microscope alone.…”

“…Then, it is hard to differentiate the ES/PNET from similar other small round blue cell tumors such as embryonal rhabdomyosarcoma, neuroblastoma, and lymphoma by a standard microscope alone. 2,9 Immunohistochemical staining is helpful in differentiating ES/PNET from other small round blue cell tumors. 2,6,9 The ES/PNET group of tumors has a common cell surface glycoprotein marker, cluster of differentiation 99 (CD99), which is a product of major histocompatibility complex class I-related ( MIC ) 2 gene.…”

“…2,9 Immunohistochemical staining is helpful in differentiating ES/PNET from other small round blue cell tumors. 2,6,9 The ES/PNET group of tumors has a common cell surface glycoprotein marker, cluster of differentiation 99 (CD99), which is a product of major histocompatibility complex class I-related ( MIC ) 2 gene. 2,3,6 And positive finding of other markers, including FLI-1, neuron-specific enolase (NSE), vimentin, also can be helpful for diagnosis of ES/PNET.…”

“…2,6 Molecular genetic techniques, such as fluorescent in-situ hybridization (FISH), reverse transcriptase polymerase chain reaction (RT-PCR) can be used for definitive diagnosis for the ES/PNET. 1,9 Identification of the t (11;22)(q24;q12) chromosomal translocation (EWS-FLI1 gene fusion) is highly specific for ES/PNET, because >90% of the tumors show this gene rearrangement. 9 …”

“…1,9 Identification of the t (11;22)(q24;q12) chromosomal translocation (EWS-FLI1 gene fusion) is highly specific for ES/PNET, because >90% of the tumors show this gene rearrangement. 9 …”