Soft tissue
Skeletal muscle
Embryonal rhabdomyosarcoma - general

Author: Erdener Özer, M.D., Ph.D.

Revised: 27 November 2017, last major update November 2017

Copyright: (c) 2002-2017, PathologyOutlines.com, Inc.

PubMed Search: Embryonal rhabdomyosarcoma [title] Review[ptyp]

Related topics: Embryonal - NOS, anaplastic, botryoid, spindle cell

Cite this page: Özer, E. Embryonal rhabdomyosarcoma - general. PathologyOutlines.com website. http://pathologyoutlines.com/topic/softtissueembryonalrhabdo.html. Accessed December 11th, 2017.
Definition / general
  • Subtype of the rhabdomyosarcoma (RMS) soft tissue cancer family whose lineage is from primitive mesenchymal cells of embryonic skeletal muscle
  • Most common RMS subtype (approximately 60 - 70% of childhood cases)
  • Embryonal RMS includes the typical (or not otherwise specified), atypical and botryoid patterns
ICD-10 coding
Epidemiology
  • Most common in children 0 - 4 years old with a maximum reported incidence of 4 cases per 1 million children
  • Rare congenital cases have also been reported
Sites
  • Usually present in head and neck region including nasal and oral cavities, orbit and middle ear as well as paratesticular region and the genitourinary tract
  • Extremity involvement is uncommon
  • Metastasizes to soft tissue, serosa, lung, lymph nodes and bone marrow
Pathophysiology
  • Derived from precursor cells within the muscle tissue
Etiology
  • Most cases occur sporadically with no genetic predisposition
  • Children with predisposing familial syndromes, in which there are defects in the Ras or Hedgehog pathways, are at higher risk for developing embryonal RMS
Prognostic factors
  • Favorable prognostic factors are younger age, botryoid variant, genitourinary location, localized tumor and hyperdiploidy
  • Presence of diffuse anaplasia is a negative prognostic factor
  • Extremity involvement is associated with more relapses and lower survival
Case reports
Treatment
  • Excision, chemotherapy, radiation therapy
  • Intergroup Rhabdomyosarcoma Study Postsurgical Clinical Grouping System is recommended to plan treatment in pediatric cases
  • AJCC TNM staging system remains appropriate for planning treatment adult patients
Gross description
  • Poorly circumscribed mass, white, soft or firm, infiltrative
Gross images

Images hosted on PathOut servers:

Images contributed by Mark R. Wick, M.D.

Orbital



Case of the Week #268 - Parotid mass

Various images



Images hosted on other servers:

White tumor mass with focal necroses

Incision of the oral mucosa

Microscopic (histologic) description
  • Composed of primitive mesenchymal cells that show variable degrees of cytoplasmic skeletal muscle differentiation
  • They are moderately cellular but in the typical pattern often contain both hypo and hypercellular areas with a loose, myxoid stroma
  • Perivascular condensations of tumor cells in the less cellular regions are common
  • Sheets of small, stellate, spindled or round cells with scant or deeply eosinophilic cytoplasm and eccentric, small oval nuclei with a light chromatin pattern and inconspicuous nucleoli
  • Many tumor cells contain generous amounts of eosinophilic cytoplasm, a feature of rhabdomyoblastic differentiation
  • May have cells with elongated tails of cytoplasm (tadpole cells) and cells with cytoplasm in the shape of a ribbon or strap
  • Cross striations in 50%
  • Dense pattern of embryonal RMS that may resemble solid alveolar RMS shows similar cytologic features, although rhabdomyoblastic differentiation is minimal (Am J Clin Pathol 2013;140:82)
  • Rare morphological appearances:
    • Anaplastic features (see anaplastic variant)
    • Rhabdoid features (epithelioid or rhabdoid-like RMS; Am J Surg Pathol 2011;35:1523)
    • Melanocytic, neuroblastic / ganglionic or schwannian differentiation (ectomesenchymoma)
    • Clear cell change
  • More differentiation typically occurs postchemotherapy or radiotherapy
Microscopic (histologic) images

Images hosted on PathOut servers:

Images contributed by Erdener Özer, M.D., Ph.D.

Various stains


Courtesy of Mark R. Wick, M.D.:

Intra-oral

Nose

Orbital

Myogenin



Case of the Week #268 - Parotid mass - gangliorhabdomyosarcoma:

Various images



Case of the Week #276 - Tonsillar mass:

Various images


Actin

Desmin

Myogenin

MyoD1



Images hosted on other servers:

Mandible

Soft palate

Cytology description
Cytology images

Images hosted on PathOut servers:

Images contributed by Erdener Özer, M.D., Ph.D.

Small round cell tumor

Positive stains
Electron microscopy description
  • Developing striated muscle, thick and thin filaments
Molecular / cytogenetics description
  • 11p15.5 loss of heterozygosity or loss of imprinting is a frequent finding
  • Chromosomal aneuploidies are very common with gains of chromosome 8 particularly common (seen in 90% of patients)
  • No diagnostic translocation found to date
  • 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 (Genes Chromosomes Cancer 2011;50:397)
  • No N-myc amplification
Differential diagnosis
Board review question #1
Which FISH testing may assist in making distinction between dense pattern of embriyonal rhabdomyosarcoma and the alveolar subtype of rhabdomyosarcoma?

  1. ETV6-NTRK3
  2. EWS-FLI1
  3. PAX-FOXO1
  4. SYT-SSX1
  5. TPM3-ALK
Board review answer #1
C. PAX-FOXO1; This fusion gene product occurs in approximately 85% of alveolar RMS cases