Soft tissue
Skeletal muscle
Embryonal rhabdomyosarcoma - general

Author: Vijay Shankar, M.D. (see Authors page)

Revised: 26 September 2016, last major update November 2012

Copyright: (c) 2002-2016,, Inc.

PubMed Search: Embryonal rhabdomyosarcoma [title]

See also: embryonal-NOS, anaplastic, botryoid, spindle cell

Cite this page: Embryonal rhabdomyosarcoma - general. website. Accessed October 19th, 2017.
Definition / general
  • Primitive soft tissue sarcoma with small blue cells resembling embryonic skeletal muscle
  • Most common rhabdomyosarcoma subtype (65%)
  • Usually in nasal and oral cavities, orbit, middle ear, prostate, paratesticular region
  • Rare in skin, thoracic cavity, esophagus and stomach
  • Metastasizes to soft tissue, serosa, lung, lymph nodes and bone marrow
  • Extremity involvemen is uncommon and associated with more relapses and lower survival
Case reports
  • Excision, chemotherapy, radiation therapy
  • Favorable prognostic factors are younger age, spindle and botryoid variants in young patients, GU location (survival of 90%+ after excision and chemotherapy), localized tumor (survival of 80%); also hyperdiploid
  • Presence of diffuse anaplasia is negative prognostic factor
Gross description
  • Poorly circumscribed mass, white, soft or firm, infiltrative
Gross images

Images hosted on PathOut servers:

Orbital, courtesy of Mark R. Wick, M.D.

Case of the Week #268

Images hosted on other servers:

White tumor mass with focal necroses

Incision of the oral mucosa

Microscopic (histologic) description
  • Composed of primitive mesenchymal cells in various stages of myogenesis
  • Sheets of small, spindled or moderate to poorly differentiated round cells with scant or deeply eosinophilic cytoplasm and eccentric, small oval nuclei
  • Highly cellular areas around blood vessels alternate with parvicellular mucoid regions (resembles normal embryonal myogenesis)
  • Cross striations in 50%
  • Rarely has anaplastic features (see anaplastic variant), clear cell change, rhabdoid features, neuronal, melanocytic or schwannian differentiation (ectomesenchymoma)
  • More differentiation typically occurs post-chemotherapy or radiotherapy
Microscopic (histologic) images

Images hosted on PathOut servers:
Courtesy of Mark R. Wick, M.D.:





Case of the Week #268:

Case of the Week #276:





Images hosted on other servers:


Soft palate

Cytology description
Positive stains
Electron microscopy description
  • Developing striated muscle, thick and thin filaments
Molecular / cytogenetics description
  • Loss of 11p15
  • +2q, +8, +12, +13, +20
  • No N-myc amplification
  • Congenital cases are associated with t(2;8)(q35;q13) involving PAX3 gene (Cancer Genet Cytogenet 2009;191:43)
  • Inactivating mutations of TP53 and CDKN2A and activating mutations of RAS family genes
  • No diagnostic translocation found to date
Differential diagnosis
  • Desmoplastic small round cell tumor: tumor nodules on serosal surfaces, strongly keratin+ and EMA+, may be desmin+ but muscle specific actin-
  • Ewing's / PNET: often rosettes, nuclei are uniform and pale, not dense and hyperchromatic; CD99+, desmin-, muscle specific actin-, t(11;22)+
  • Large cell lymphoma: CD45+, B/T cell markers present, desmin-, muscle specific actin-
  • Neuroblastoma: elevated urinary catecholamines, rosettes, granular chromatin, S100+ (often), chromogranin+, GFAP+
  • Rhabdomyoma
  • Undifferentiated sarcoma: negative for muscle markers