Pathology of Rhabdomyosarcoma
Embryonal Rhabdomyosarcoma :
Age and site: Usually occurs in children (before the age of 10 years).
Common sites include head and neck region, genitourinary tract and retroperitoneum.
Alternating cellular and myxoid areas.
Classical form is composed of undifferentiated round or spindle cells together with a few scattered eosinophilic rhabdomyoblasts.
Some elongated rhabdomyoblasts show angulation of muscle fibres (broken straw sign).
Multivacuolated or spider web cells may be present.
Cytoplasmic cross striations are noted in about 20-30% cases.
Intracellular glycogen is more prominent in well-differentiated forms.
Immunohistochemistry plays an important role in establishing the diagnosis.
Desmin and muscle actin are positive.
and myogenin (myf4) are also useful markers.
Located in mucosa lined hollow organs. Example: Nasal cavity, nasopharynx, bile duct, urinary bladder and vagina.
Grossly, the tumour has a polypoid grape like appearance.
Microscopically the tumour arises in the submucosa and is covered by hyperplastic epithelium.
Subepithelial cambium layer composed of condensed undifferentiated tumour cells is a characteristic feature.
The rest of the tumor consists of a relatively sparse population of cells in a backround of mucoid stroma.
Scattered spindle shaped or
rounded rhabdomyoblasts may be present.
Located in the paratesticular region (rarely head & neck region).Characterized by eosinophilic spindle cells arranged in a fascicular or storiform pattern.
Characterized by areas of bizarre cell with giant nuclei in a collagenous backround, together with foci of identifiable embryonal areas.
Atypical mitotic figures are present.
Alveolar pattern - The tumour consists of aggregates of undifferentiated tumour cells arranged in a alveolar pattern.
Eosinophilic rhabdomyoblasts and giant cells with peripheral wreath-like nuclei are prominent.
The cellular aggregates are separated by dense hyalinized fibrous septa.
The tumour cells at the periphery are well preserved.
The cells at the centre of the alveolar spaces are loosely arranged and poorly preserved.
Cross striations are noted in only 10% cells.
Solid pattern - Solid packed masses of tumour cells resembling round cell areas of embryonal rhabdomyosarcoma (may resemble carcinoma or malignant melanoma).
A microalveolar pattern has also been described.
Demonstrate strong and widespread myogenin expression compared to embryonal type.
The majority of the alveolar rhabdomyosarcomas are associated with specific chromosomal translocations (pARMS).
Because alveolar variant is much more aggressive than embryonal variant, RMS subclassification has clinical relevance.
Pleomorphic Rhabdomyosarcoma :
is considered rare and controversial.
Pathological features - The tumour consists of large polygonal or spinde shaped rhabdomyoblasts. The backround stroma is collagenous.
Storiform areas may be present.
The tumour cells contain glycogen.
Cells with cross striations are usually absent.
Rare variant: Sclerosing Rhabdomyosarcoma-
It is not clear where this variant belong in the current classification of Rhabdomyosarcoma.
Site: Usually located in the extremities.
Characterised by prominent hyaline sclerosis and a pseudovascular growth pattern.
Microscopic features: Histologically, the neoplasms are composed of round/polygonal and spindle-shaped tumour cells including typical rhabdomyoblasts.
The cells are primitive appearing with scanty eosinophilic cytoplasm and irregular nuclear outline and coarse chromatin.
The stroma divides the tumour mass into lobules and small nests.
Tumour cells stained positively for desmin (focal and sometimes dot-like), strongly positive for smooth muscle actin (HHF35) and also for markers of striated muscle differentiation (myogenin, MyoD1).
Cytogenetics play an important role in confirming the diagnosis rhabdomyosarcoma.
Alveolar rhabdomyosarcoma is associated with a specific translocation, t(2;13)(q37;q14) or its variant t (1;13)(p36;q14).
Embryonal rhabdomyosarcoma often shows loss of heterozygosity for 11p, but there is no specific cytogenetic or molecular marker comparable to those for alveolar Rhabdomyosarcoma.
Mimics of Rhabdomyosarcoma:
International Classification of Rhabdomyosarcoma:
Superior prognosis: Botryoid Rhabdomyosarcoma ; Spindle cell Rhabdomyosarcoma
Intermediate prognosis: Embryonal Rhabdomyosarcoma
Poor prognosis: Alveolar Rhabdomyosarcoma ; Undifferentiated sarcoma
The combination of histology, immunohistochemistry, chromosome analysis, and molecular cytogenetics played an important role in the diagnosis of Rhabdomyosarcoma.
of DNA Ploidy and Proliferative Index (MIB-1 Index) in Childhood
Rhabdomyosarcoma and undifferentiated sarcoma in the first two decades of life: a selective review of intergroup rhabdomyosarcoma study group experience and rationale for Intergroup Rhabdomyosarcoma Study
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