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RESIDENT
CASE
STUDIES
Week 4 May 12 - May 16, 2003: Case
3
Table
of Contents | List of Diagnoses | Case 1 | Case 2 |
Case
3 | Case 4
22
year old Caucasian male with left clavicular lesion
Discussion:
Ewing’s sarcoma is a common malignant bone tumor occurring in children
and young adults from age 5-20 years. It is slightly more common in males
than females ( ratio 1.5:1). The tumor can affect any bone, but the most
common sites are in the lower extremities (45%), followed by the pelvis
(20%), the upper extremity (13%), the axial skeleton and ribs (13%), and
the face (2%). Midshaft of the femur is the most frequent location for
this tumor.1
Histologically, the tumor
consists of small round cells with regular round nuclei containing finely
dispersed chromatin and inconspicuous nucleoli, and a narrow rim of clear
or pale cytoplasm. Immunohistochemical stain is usually positive for
MIC-2(CD99) which is helpful in diagnosis to distinguish it from other
small round cell tumors.
Translocation of chromosomes
t(11,22)(q24,q12) has been identified in this tumor and in PNET suggesting
they may belong to the same Ewing’s sarcoma family of tumor. The most
commonly associated cytogenetic change is t(11,22)(85%), involving the EWS
gene on 22q12 and FLI1 gene on 11q24, which
results in a chimeric fusion transcript EWS-FLI1. Other gene
rearrangements (15%) are also identified in Ewing’s sarcoma such as:
t(21;22)(q22;q12), t(7;22)(p22;q12), t(17;22)(q21;q12), t(2,22)(q33;q12),
t(11,14,22)(q24;q11;q12) and t(10;11;22)(p11.2;q24;q12).
Cytogeneytics, FISH and RT-PCR are useful techniques in detecting
the translocation.1
Ewing's sarcoma must be
differentiated from other small round blue cell tumors by
immunohistochemistry and cytogenetics.
References:
1Burchill, SA.
Ewing's sarcoma: Diagnostic, prognostic and therapeutic implications of
molecular abnormalities. J. Clin Pathol 2003;56:96-102.
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