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RESIDENT
CASE
STUDIES
Week 4 May 12 - May 16, 2003: Case
4
Table
of Contents | List of Diagnoses | Case 1 | Case 2 |
Case
3 | Case 4
22
year old woman with a right cheek mass (8cm)
Discussion:
Rhabdomyosarcoma, the largest category of soft tissue sarcomas in children
and adolescents, is a malignant soft tissue sarcoma with features of
embryonic skeletal muscle. It is uncommon in adults. There are 3 main
types of rhabdomyosarcoma: embryonal,
alveolar and pleomorphic. The
discussion on alveolar and pleomorphic variants of rhabdomyosarcoma will
be given at a subsequent Residents’ conference.
Embryonal
rhabdomyosarcoma, the
diagnosis in this case, is the most common type of rhabdomyosarcoma,
affecting infants and children.
There
are 3 variants of embryonal rhabdomyosarcoma:
spindle cell, botyroid and anaplastic. It
is therefore, not sufficient just to make a diagnosis of rhabdomyosarcoma.
The type/variants must be stated.
The
greatest proportion of cases occur within the head and neck (orbit,
eyelid, parotid, nasopharynx, tongue, cheek, etc.) followed by the
genitourinary system. Less than 9%
of the cases of rhabdomyosarcoma arise in skeletal muscle. The spindle
cell variant of embryonal rhabdomyosarcoma usually arises in the scrotal
soft tissue in children, but in non-paratesticular locations in adults.
Botyroid variant of embryonal rhabdomyosarcoma on the other hand, by
definition, must arise beneath a mucosal epithelial surface.
The
histology is usually reminiscent of small round blue cells in typical
cases. Primitive mesenchymal cells in various stages of myogenesis are
seen. Differentiation may be seen with cells acquiring more cytoplasmic
eosinophilia and elongate shapes (strap cells, tadpole cells and spider
cells). Differentiation may not be obvious.
Botyroid
variant may have alternating areas of dense and loose cellularity,
and this varies from case to case. There is often a cambium layer
(aggregates of tumor cells that tightly abut an epithelial surface). This
variant may also contain an abundant, loose, myxoid stroma that can appear
deceptively benign. The cambium layer in not seen in this case, probably
because the biopsy does not include the epithelial layer.
The
spindle cell variant may
resemble smooth muscle cells
(but may have cytoplasmic cross striation). It may also have a storiform architecture
similar to fibrous histiocytoma or a wavy character like neurofibroma.
Immunohistochemistry will help in this case.
Anaplastic
variant has obvious
pleomorphism with hyperchromatic nuclei and atypical mitosis.
Antibodies
against MyoD1 (only nuclear stain
counts as shown in image 4 ) and myogenin (nuclear) are highly
specific and sensitive for rhabdomyosarcoma and they are currently used as
standard antibodies for diagnosis. Rhabdomyosarcoma, usually stains for
vimentin (cytoplasmic), desmin and muscle specific actin (HHF-35). Desmin
and HHF-35 are neither sensitive nor specific, and may be shared by smooth
muscle, cardiac muscle, cardiac muscle, myofibroblasts, myoepithelial
cells, pericytes and some mesothelial cells. Aberrant staining with a
variety of immunohistochemical markers like cytokeratin, S100 and CD20 are
also seen.
There
is complex cytogenetic abnormality in embryonal rhabdomyosarcoma. There
may be an allelic loss in the chromosomal region 11p15 in most embryonal
rhabdomyosarcoma. The
t(2;13)(q37;q14) is seen in alveolar rhabdomyosarcoma and not
in
embryonal rhabdomyosarcoma.
Prognosis
can be determined by stage, histologic classification (embryonal better
than alveolar; spindle cell/botyroid variant better than anaplastic), age,
site of origin. Histologic subtypes in adults appears to have no
prognostic relevance.
References:
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Fletcher C.D.M., Unni
K.K., Mertens F. (Eds): World Health Organization Classification of
Tumours. Pathology and Genetics of Tumors of Soft Tissue and Bone.
IARC Press: Lyon 2002
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