Pleomorphic rhabdomyosarcoma is a type of rhabdomyosarcoma, and is the least common, accounting for only 5% of all rhabdomyosarcomas. Unlike embryonal and alveolar types, these tumours occur in adults over the age of 40 years 1 and are difficult to distinguish from other pleomorphic sarcomas such as malignant fibrous histiocytomas 2.
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Pathology
Some publications divide into three specific types 3:
classic: predominantly atypical pleomorphic polygonal rhabdomyoblasts (PRMB) in sheets
round cell: clusters of PRMB throughout the tumour with a background of slightly atypical, medium-sized, round, blue RMB
spindle cell: scattered PRMB in a predominance of atypical spindled RMB arranged in a storiform growth pattern
Location
They typically occur in the limbs, with a predilection for the thigh 2.
Immunophenotype
Immunohistochemistry can reveal the following to varying proportions ref:
myoglobin: common
MyoD1
skeletal muscle myogenin (myf4)
fast skeletal muscle myosin
desmin
muscle-specific actin
smooth muscle actin (SMA)
muscle-specific myogenin (myf3)
Radiographic features
The features are non-specific (see radiographic features in the parent article: rhabdomyosarcoma), although in general pleomorphic rhabdomyosarcomas have multiple areas of necrosis. In some instances, these areas are surrounded by pronounced ring-like enhancement 1.
Treatment and prognosis
They are considered a high-grade sarcoma with an aggressive clinical course 3.
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