Maturation toward neuronal tissue in a Ewing sarcoma of bone after chemotherapy

Background Ewing sarcoma is the second most common bone tumor, occurring mainly in children and young adults. It shows a typical primitive, small round cell morphology and a characteristic fusion oncogene involving EWSR1 and members of the ETS family in most of the cases. Neuronal maturation after chemotherapy is a rare phenomenon and we herein describe such an exceptional case. Case presentation An 8-year old boy was diagnosed with a Ewing sarcoma in the left femur. On biopsy the morphology was typical and there was an EWSR1-FLI1 gene fusion. He underwent neo-adjuvant chemotherapy and resection of the tumor. On microscopic evaluation, part of the tumor showed ganglioneuroblastoma-like differentiation with expression of neuronal markers. The continued presence of EWSR1 rearrangement in both the blue round cell component and the ganglioneuroblastoma-like component was shown by FISH analysis. Conclusions In conclusion, this case describes the possibility of a Ewing sarcoma to differentiate into a ganglioneuroblastoma-like lesion after neo-adjuvant chemotherapy treatment; the prognostic value of this phenomenon remains questionable. Electronic supplementary material The online version of this article (doi:10.1186/s13000-016-0516-0) contains supplementary material, which is available to authorized users.


Background
Ewing sarcoma, first described by James Ewing in 1921, is the second most common malignant bone tumor after osteosarcoma. Occurring mainly in children and young adults; it accounts for 3 % of childhood malignancies. During the last decades, the 5 year overall survival has improved up to 85 % for patients with localized disease but is still only 30 % for patients with metastatic disease [1,2]. Ewing sarcomas are primitive small blue round cell tumors of bone and soft tissue, characterized by the expression of EWS-ETS fusion genes as a driver mutation [3,4].
Neural differentiation in Ewing sarcoma is a rare phenomenon and has been described before in a few cases [3,5]. Here we present a case in which an Ewing sarcoma shows ganglioneuroblastoma-like differentiation after chemotherapeutic treatment.

Case presentation
An 8-year old boy with no previous relevant medical history, presented with pain and a palpable mass in the left upper thigh. MRI showed a ca. 10 cm large lesion in the femur with soft tissue extension. There were no signs of metastasis elsewhere. The patient received neoadjuvant chemotherapy by the Ewing 2008 protocol. After 4 cycles of VIDE (vincristine, ifosfamide, doxorubicin and etoposide) chemotherapy, a staging FDG-PET/CT-scan was performed, showing tumor regression, however no normalization of metabolic activity at the primary tumor site. After 6 cycles of VIDE, resection of the femur diaphysis was performed with reconstruction with a vascularised fibula transplant. An optimal recovery has been seen so far, with no sign of recurrence or metastatic disease at 21 months after surgery.

Histology Biopsy
The pretreatment biopsy (routinely formalin-fixed, paraffin-embedded, decalcified and hematoxylin-eosin-stained) revealed microscopically a small blue round cell tumor with necrosis. A panel of antibodies was applied according to standard protocol (antibodies used can be seen in Additional file 1). There was positive membranous staining for CD99 and CD56, consistent with the diagnosis of Ewing sarcoma. By RT-PCR, the presence of the EWSR1-FLI1 fusion gene confirmed this diagnosis. including NF, Neu-N and GFAP. There was no S100 expression (Fig. 2). To confirm the continued presence of the fusion gene FISH analysis was performed showing rearrangement of EWSR1 in both the small blue round cell component and the ganglioneuroblastomalike component.

Discussion
The cellular origin of Ewing sarcomas remains both elusive and controversial. However, the immature neural phenotype of many tumors, formerly known as PNET [5,6], along with their gene expression signatures and their disposition to neural differentiation in experimental models implicate a neural crest stem cell genetic program as integral feature of pathogenesis of Ewing sarcoma [7]. Therefore, it is not surprising that patient material, at least in some cases, show (ganglio) neuroblastoma-like morphology.
Delattre et al. and Burchill et al. described neuroblastomalike features in a few untreated Ewing sarcoma cases with genetic confirmation [8,9], which could be a diagnostic pitfall.
On the other hand, our case and the reported cases by  [3].
However, such cases are very rare, we didn't find another one when reviewing 26 cases from our archives. This is in line with the results of Delattre et al. investigating a series of more than 90 cases with two neuroblastoma-like instances [8].
Maturation during chemotherapeutic treatment is a more common finding in other primitive pediatric tumors such as rhabdomyosarcoma and neuroblastoma [10][11][12][13]. Since neural maturation is very rare in Ewing sarcoma, the prognostic value remains unclear in comparison to e.g., embryonal rhabdomyosarcoma where it is associated with favorable outcome [10,14]. At least the case by Maeda et al. had a unfavorable outcome with metastatic disease showing typical small blue round cell morphology of Ewing sarcoma in contrast to our case with no signs of recurrence or metastases at 21 month after surgery [5].

Conclusions
In conclusion, this case describes the possibility of a Ewing sarcoma to differentiate into neural tissue after neo-adjuvant chemotherapy treatment, the prognostic value of this phenomenon remains questionable.