rhabdomyosarcoma is a rare variant of Rhabdomyosarcoma.
(Note: Rhabdomyosarcoma comprises a group
of malignant soft tissue tumours with skeletal muscle differentiation.)
(2) It was first described in 2000 by
Mentzel and Katenkamp.
They described three cases of rhabdomyosarcoma in
adult patients, characterized by prominent hyaline sclerosis and a
pseudovascular growth pattern, and called it "sclerosing, pseudovascular
(3) In 2002, Folpe
et al. also described four cases of an
unusual hyalinizing, matrix-rich variant of RMS. They named it "sclerosing
(4) Sclerosing rhabdomyosarcoma is
an exceedingly rare tumour and it is still debated whether it is a
distinct variant of rhabdomyosarcoma or a subtype of embryonal or alveolar
(5) Microscopically, the neoplastic
cells are arranged into lobules, small nests, microalveoli and even
single-file arrays in an abundant hyalinized, eosinophilic to basophilic
matrix that closely resembles primitive osteoid or chondroid material.
mitotic rate is very high.
In some cases tumor cells focally display the cribriform pattern closely mimicking adenoid cystic carcinoma.
(6) The tumour is strongly positive for
Vimentin, Desmin and MyoD1, and weakly, focally positive for Myogenin
suggesting its skeletal muscle differentiation, but negative for
cytokeratin, S-100, CD34, and CD31. Some cases can also show positive
expression of CD99, SMA and CD56.
Differential diagnosis of Sclerosing
rhabdomyosarcoma includes osteosarcoma, extraskeletal myxoid
chondrosarcoma, mesenchymal chondrosarcoma, sclerosing epithelioid
fibrosarcoma, angiosarcoma, parachordoma and even metastatic carcinoma.
is important for pathologists to be familiar with Sclerosing
rhabdomyosarcoma, because it potentially may be mistaken for other
typical osteosarcoma is characterized by the presence of matrix
myxoid chondrosarcoma typically forms a well circumscribed,
multilobulated architecture separated by incomplete fibrous septa. It
is composed of round or slightly elongated cells of uniform shape and
size usually arranged in short anastomosing strands or cords in myxoid
chondrosarcoma is characterized by distinct undifferentiated tumour
cells admixed with well differentiated cartilagenous components.
epithelioid fibrosarcoma is composed of epitheloid cells arranged in
nests and cords and deposited in a densely hyalinized collagenous
matrix. However, in almost all cases the tumor also shows foci of
spindle-shaped sarcoma similar to conventional fibrosarcoma.
- Angiosarcoma : Sclerosing
rhabdomyosarcoma focally may also form anastomosing vascular and
gland-like spaces mimicking angiosarcoma, but angiosarcoma lacks
characteristic hyalinizing matrix of sclerosing
- Parachordoma is
typically lobulated and contains nests of vacuolated cells deposited
in a myxoid matrix, resembling the physaliphorous cells of chordoma.
It usually expresses S-100 protein and CK simultaneously.
carcinoma : Positive expression of Desmin and MyoD1, negative
expression of CK can also rule out the possibility of metastatic
(8) The prognosis
rhabdomyosarcoma in adults is significantly worse than the pediatric population.
The rate of
recurrence and metastasis is about 40-50%.
The prognosis of
tumors located in the head and neck are poorer than those located in