What are the histologic characteristics of embryonal rhabdomyosarcoma?

Updated: Feb 01, 2019
  • Author: Amelia F Drake, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Embryonal rhabdomyosarcoma is the most common subtype observed in children, accounting for approximately 60% of all cases in this age group. The tumors can occur at any site, but they are most commonly observed in the genitourinary region or the head and neck region. On histologic examination, they have high cytologic variability, which represents several stages of skeletal muscle morphogenesis. They may range from highly differentiated neoplasms containing rhabdomyoblasts with large amounts of eosinophilic cytoplasm and cross striations similar to that of poorly differentiated tumor cells (see the image below). Desmin and muscle specific actin are the typical stains used to identify rhabdomyosarcoma. Newer staining agents, such as myogenin and MyoD1, are more specific for skeletal muscle than older stains. Desmin and actin stain smooth muscle as well.

Embryonal rhabdomyosarcoma is evidenced by a varia Embryonal rhabdomyosarcoma is evidenced by a variable cell population consisting of small, round tumor cells with hyperchromatic nuclei and of large, polygonal-shaped tumor cells with abundant eosinophilic cytoplasm, which often contains diagnostic cross striations (arrow). Image provided by Scott Kilpatrick, MD, Department of Pathology, University of North Carolina Hospitals.

Embryonal rhabdomyosarcoma has unique molecular characteristics. Embryonal rhabdomyosarcoma cells show a loss of specific genome material from the short arm of chromosome 11. This consistent loss of the material from the 11p15 region may suggest the presence of a tumor suppressor gene, though the actual gene responsible for embryonal rhabdomyosarcoma is not yet known. Another molecular feature is its lack of gene amplification. In addition, the cellular DNA content of embryonal rhabdomyosarcoma is hyperdiploid (1.1-1.8 X normal DNA). [8]


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