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RESIDENT
CASE
STUDIES
Week 3 May 5 - May 9, 2003: Case 1
Table
of Contents | List of Diagnoses | Case 1 | Case 2 |
Case
3 | Case 4
3
year old caucasian male with right arm mass. Radiography consistent with
Ewing sarcoma
Discussion:
Osteosarcoma
Osteosarcoma is the most common, non hematopoietic, primary malignant bone
tumor, in which the neoplastic cells produce osteoid, even if only in small
amounts. It occurs most frequently in young adults (with slight male
preponderance). The peak incidence is in the second decade of life.
The metaphysis of the long
bones of the appendicular skeleton, in particular, distal femur,
proximal tibia and proximal humerus are mostly affected.
The diaphysis may also be affected, but involvement of the epiphysis is rare. The radiographic appearance of conventional osteosarcoma is
extremely variable. However, in most cases, it is a mixed lytic/blastic
lesion accompanied by cortical destruction and tumor extension into soft tissue. Tumor and periosteal interaction may lead to a variety of
manifestations secondary to periosteal elevation (e.g. Codman’s
triangle).
Histologically, the neoplastic cells
tend to be highly anaplastic and pleomorphic with epithelioid,
plasmacytoid, fusiform, ovoid, small round cells, clear cells, spindle
cells, mono or multinucleated giant cells. Most cases, however, have complex mixtures of two or more of these cell types.
Tumoral osteoid must be identified in order to make a diagnosis of
osteosarcoma (Tumoral osteoid appears as a fine lacelike network,
sheets, or interlacing trabeculae). Osteosarcoma can also produce varying
amounts of cartilage and/or fibrous tissue. Some investigators further
subdivide osteosarcoma based on the matrix (chondroblastic, fibroblastic
and osteoblastic).
There are complex cytogenetic
aberations. Amplifications at 1q21-23 and at 17p are frequent findings in
conventional osteosarcoma. In aggressive osteosarcomas CDK4 is most
consistently amplified. Overexpression of MET and FOS has been reported in
more than 50% of osteosarcoma cases, while MYC is expressed in less than
15% of cases. There is no specific immunohistochemical or electron
microscopic findings.
Aggressive local growth and rapid
hematogenous spread mark its course. Osteosarcoma most frequently
metastasize to the lungs. Currently, response to pre-operative therapy is
the most sensitive indicator of survival. It must be recognized, however,
that a single system does not apply to all cases.
Typical osteosarcoma will not be
confused with other bone lesions as long as one:
-
Finds areas of tumoral bone formation even when the matrix is
chondroblastic or fibroblastic.
- Differentiates between osteoid/tumoral bone from reactive bone
formation. Reactive bone usually has the regular structure of bone with
osteoblastic rimming with loose/vascular stroma.
In this particular case Ewing
Sarcoma is a differential diagnosis because radiography suggests it, but there is a lack of
radiograhic and histopathologic correlation. Once
again, never make the diagnosis of a bone tumor in a vacuum, always get
the radiographic film / report. Be very cautious if there is a lack of
correlation between radiology and histology.
Ewing
Sarcoma: Usually a disease of children, with more than 80% of cases in patients
less than 20 years. It is uncommon after 30 years. Radiographically, it is
an ill defined osteolytic lesion involving the diaphysis of a long tubular
or flat bone, with a “moth” eaten bone destruction often associated
with “onion skin” periosteal reaction. Histologically, it has the
appearance of a small blue round cell tumor and no chondroblastic
differentiation is present. CD99, although present in almost all cases of
Ewing Sarcoma, may be focally positive in osteosarcoma.
Reference:
Fletcher,
CBM, Unni, KK, Mertens, F (Eds.): World Health Organization Classification
of Tumors. Pathology and Genetics of Tumors, Soft Tissue and Bone. IARC
Press: Lyon 2002.
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