Therapy-Induced Neural Differentiation in Ewing's Sarcoma: A Case Report and Review of the Literature
Kıvılcım Eren ERDOĞAN1, Mehmet Ali DEVECİ2 , Zeynep Ruken HAKKOYMAZ1, Gülfiliz GÖNLÜŞEN1
1Department of Pathology, Cukurova University Faculty of Medicine, ADANA, TURKEY
2Department of Orthopedics Surgery and Traumatology, Cukurova University Faculty of Medicine, ADANA, TURKEY
Keywords: Ewing's sarcoma, Therapy, FISH, EWSR1, Neural differentiation
Ewing's sarcoma (ES) is a small round cell tumor of adolescents or young adults that usually arises in the deep soft tissues of the extremities.
The tumor cells have uniform round nuclei, fine powdery chromatin and indistinct nucleoli. CD99 (O13) is a product of the MIC 2 gene
that is highly sensitive to ES but not specific. A panel of markers should be used for the differential diagnosis of small round cell tumors
because nearly all others, on occasion, show membranous staining for CD99. One of the defining feature of ES is the presence of 22q12 gene
rearrangement. The presented case is a 6 year-old boy complaining of swelling on his right leg. The biopsy was compatible with classic ES
in terms of histopathological, immunohistochemical and cytogenetic criteria. Wide surgical resection was performed after chemotherapy.
The posttreatment specimen was composed of uniformly small round cells mixed with areas of ganglion cells embedded in neurophil-like
fibrillary background. Immunohistochemically, neoplastic cells revealed strong CD99 (O13) and NSE staining and the tumor had EWSR1 gene
rearrangement. Morphologic alterations due to treatment are commonly seen in pediatric tumors. Single case reports have defined neural
differentiation in ES but to the best of our knowledge this is the first report of ES in the literature with all histopathological, immunohistochemical,
and cytogenetic criteria evaluated in both pretreatment and posttreatment specimens.
Ewing’s sarcoma (ES) represents 6% to 8% of all primary
malignant bone tumors. Young adults and children are those
most commonly affected. Radiological features include an
infiltrative, ill-defined lesion and bone destruction and
periosteal reaction of the diaphysis of a long tubular or
flat bone. ES is composed of small round cells with scant
cytoplasm and indistinct cytoplasmic borders. Nearly
all tumors show immunohistochemical positivity for
CD99 (O13). This group of tumors contains a 22q12 gene
and may exhibit rosette-like structures
and/or variable markers of neural differentiation (excluding
ganglion cells) with a fibrillary background2
. The aim of
this case presentation and literature review was to discuss
the characteristics and treatment for ES.
A 6-year-old Syrian boy presented to another university
hospital with a mass in his right thigh and inability to
bear weight for the last 6 months in October 2013. A trucut
biopsy was performed and ES without any metastases
diagnosed at that center. The patient underwent neoadjuvant
chemotherapy with the VIDE protocol for 4 months. After
neoadjuvant chemotherapy, the patient had been referred
to our center for surgical treatment. Radiological staging of the patient had been done and a lytic-sclerotic lesion
of the entire femoral diaphysis causing a partially healed
pathological fracture with a massive soft tissue mass which
had extensive sunburst-like calcifications of soft tissue and
formation of a Codman triangle involving the full length of
the femoral diaphysis (Figure 1A-C
). Magnetic resonance
imaging of the thigh showed a huge soft tissue mass
involving both anterior and posterior compartments with
central necrosis and heterogeneous contrast enhancement
originating from the femoral diaphysis, from the proximal
femoral metaphysis (without physeal involvement) to the
entire femoral diaphysis and the distal physis (Figure 2A,B
No sign of metastasis was seen in PET/CT and bone scan
). The pathological specimens were reviewed again
at our pathology department. The tumor was composed
of uniform small round cells with fine chromatin and
scant cytoplasm with diffuse immunopositivity to CD99
(O13; 1:50; Biogenex, Fremont, CA, USA); but negative to
leukocyte common antigen (LCA) (1:100; Dako, Glostrup,
Denmark), desmin (1:50; Dako, Glostrup, Denmark), and
myeloperoxidase (MPO) (1:300; Leica, IL, USA), terminal
deoxynucleotidyl transferase (TDT) (1:50; Dako, Glostrup,
Denmark). Vysis LSI EWSR1 (22q12) Dual Color Break
Apart Rearrangement Probe (Abbott, Des Planes, IL, USA)
was used to detect tumor cells with one green and one orange signal (Figure 4A,B
). The EWSR1 gene rearrangement was
detected by fluorescence in situ hybridization (FISH) in
this biopsy. The tumor was interpreted as ES. The patient
was discussed at the musculoskeletal oncology council
and because of extension of the disease through the whole
femoral diapysis with a huge soft tissue mass, the age of the
patient and the patient’s socioeconomic status (he was an
Syrian immigrant living in an immigrant camp and unable
to have the adequate follow-up after a complex biological
reconstruction), a hip disarticulation was performed in
February 2014. Grossly, a 15×7×7 cm tumor mass was
detected. Necrotic areas represented 5% of the whole lesion. The viable tumor was composed of uniformly small
round cells mixed with areas of ganglion cells embedded
in a neurophil-like fibrillary background. The surgical
margins were negative. Immunohistochemistry (IHC)
revealed strong expression of CD99 and patchy expression
of neuron-specific enolase (NSE) (1:200; Dako, Glostrup,
Denmark), but not LCA, desmin, neuroblastoma marker
(Nb84a; 1:100; Leica, New Castle, UK), or MPO. The
EWSR1 gene rearrangement was detected by fluorescence
in situ hybridization (FISH) in the surgical material (Figure
). The patient completed the adjuvant chemotherapy
in September 2014. After a follow-up of 1 year, the patient is alive with no evidence of the disease and is able to walking
with two crutches.
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|Figure 1: A) Clinical
view of the patient.
B) AP and
C) Lateral radiography
of the right femur
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|Figure 4: A) Initial tru-cut biopsy showing uniformly small round neoplastic cells with scant cytoplasm (H&E; x40). B) Initial biopsy,
EWSR1 gene rearrangement transcript (FISH; x600).
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|Figure 5: A) Surgical specimen showing small round cells intermingled with ganglion cells and fibrillary background (H&E; x40).
B) Surgical specimen, EWSR1 gene rearrangement transcript (FISH; x600).
Morphologic alterations due to chemotherapy are commonly
seen in pediatric tumors such as rhabdomyosarcomas,
osteosarcomas, and Wilms’ tumors3-5
. Some studies
have indicated that complete neural differentiation in ES
may be due to treatment6-9
We have herein presented a case of classic alteration of
ES with areas of ganglion cells and a fibrillary neurophillike
background intermingled with small round cells after
four courses of chemotherapy. Both pretreatment and
posttreatment specimens showed CD99 immunopositivity
and presence of the EWSR1 gene rearrangement. This
case differs from other cases in the literature because the
morphological, immunohistochemical, and molecular
features of the ES persisted after therapy. Maeda et al.7
presented a case involving widespread replacement of an ES
by a tumor with a lower MIB-1 index and neuroendocrine
differentiation composed of ganglion cells following
preoperative chemotherapy and radiotherapy. Knezevich
et al.8 presented an extraosseous ES that exhibited a
well-differentiated neural tumor composed of ganglion
cells following chemotherapy and radiotherapy. The initial
biopsy showed EWS/FLI1 fusion, but wide resection
lacked the EWS/FLI1 fusion transcript. Collini et al.10
presented a case of CD99-positive ES; after treatment, the
surgical specimen lacked CD99, resembling differentiating
neuroblasts. Both pretreatment and posttreatment
specimens showed the EWS/FLI1 gene fusion transcript,
the hallmark of ES (Table I).
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|Table I: Therapy-induced clinical, pathological, immunohistochemical and molecular features of Ewing’s Sarcoma cases published in
The possible scenarios of neural differentiation in ES are
1. Cells with neural differentiation survive. Primitive
round cells are killed by cytotoxic drugs7.
2. Chemotherapeutic drugs induce active neural
differentiation in tumor cells7.
3. Slowly growing clones of the primary tumor lacking the
EWS/FLI1 gene fusion transcript are less sensitive to
chemotherapy and radiation8.
4. Neural differentiation could represent a direct
phenotypic feature of surviving cells or may be induced
5. EWS/FLI1 and related oncoproteins may inhibit neural
differentiation and maintenance of cells in a proliferative
state within the cell cycle8.
Collini et al. and Maeda et al. reported the EWS/FLI1
gene fusion transcript following therapy7,10. However,
the patient described herein contained the EWSR1 gene
rearrangement; therefore, the results are not consistent
with the suggestion by Knezevich et al.8. Our patient’s
initial and post CT-RT specimen exhibited CD99-positive
staining and presence of the EWSR1 gene rearrangement
transcript. From this aspect, this case differs from the other
cases in terms of the IHC and cytogenetic features.
Our patient’s surgical specimen contained neural cells
following therapy, which is consistent with hypotheses #2
and #4 described above. Furthermore, he had the same
IHC and FISH results regardless of therapy. The best of
our knowledge this is the first report of ES in the literature
with all histopathological, immunohistochemical, and
cytogenetic criteria in both pretreatment and posttreatment
specimens. Pathologists must be aware of therapy-induced
alterations to avoid misdiagnosis of these tumors.
CONFLICT of INTEREST
The authors have no conflict of interest to declare.
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