Breast malignant
Sarcoma
Rhabdomyosarcoma


Topic Completed: 1 February 2017

Revised: 19 September 2019

Copyright: 2002-2019, PathologyOutlines.com, Inc.

PubMed Search: rhabdomyosarcoma breast

Emily S. Reisenbichler, M.D.
Page views in 2018: 950
Page views in 2019 to date: 844
Cite this page: Reisenbichler ES. Rhabdomyosarcoma. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/breastmalignantRMS.html. Accessed October 20th, 2019.
Definition / general
  • Malignant neoplasm with skeletal muscle differentiation
Essential features
  • Comprises less than 3% of all adult primary soft tissue sarcomas and exceedingly rare as a primary breast tumor
  • Primary rhabdomyosarcoma of the breast is most commonly alveolar subtype and is seen more frequently in the pediatric / adolescent population (Med Pediatr Oncol 1997;29:181)
  • Typically composed of small, round to spindled cells, with eosinophilic cytoplasm, some of which show cytoplasmic cross striations (embryonal and alveolar subtypes); larger cells with greater degree of atypia seen in pleomorphic subtype
  • Must exclude other tumor types with heterologous rhabdomyosarcomatous differentiation (such as malignant phyllodes)
Clinical features
  • Primary rhabdomyosarcoma of the breast is seen most frequently in the pediatric / adolescent population and therefore is not typically identified by routine screening mammography
  • Presents as a palpable, circumscribed, rapidly growing mass
  • Presentation as a metastasis from a primary rhabdomyosarcoma elsewhere in the body occurs in 3 - 6% cases and portends a very poor prognosis (J Pediatr Hematol Oncol 2017;39:62)
Radiology description
  • Due to the breast density of the pediatric and adolescent population, ultrasound is the imaging modality of choice for radiographic characterization of this tumor type (Eur J Radiol 2003;48:282)
  • Hypoechoic, round or lobulated nodule / mass by ultrasound
Prognostic factors
  • Patients with primary breast alveolar rhabdomyosarcoma have a poor prognosis, frequently dying of disease with disseminated metastases (J Pediatr Hematol Oncol 2017;39:62)
  • Embryonal subtype portends much better prognosis than alveolar or pleomorphic subtypes
Case reports
Treatment
  • As with all primary breast sarcomas, wide excision without axillary dissection is the mainstay of treatment
  • Adjuvant or neoadjuvant radiation often used in large or incompletely resected tumors
  • Utility of chemotherapy is unclear due to the rarity of this tumor type
Clinical images

Contributed by Dr. Mark R. Wick

Alveolar

Gross description
  • Circumscribed, nonencapusulated mass
Gross images

Images hosted on other servers:

Large fungating mass involving right breast

Large firm lobulated tumor

Microscopic (histologic) description
  • 3 microscopic subtypes:
    • Alveolar: sheets of small, round cells clustered with variable amounts of fibrous septa; may contain scattered giant cells
    • Embryonal: cytologically round to spindle cells with scant cytoplasm in a myxoid background; elongated cells with more abundant eosinophic cytoplasm referred to as "strap" cells or "tadpole" cells
    • Pleomorphic: sheets of large cells demonstrating marked nuclear atypia or "anaplasia" with eosinophilic cytoplasm
Microscopic (histologic) images

Contributed by Dr. Mark R. Wick

Alveolar

Alveolar with differentiation

Embryonal



Images hosted on other servers:

Pleomorphic cells with thin walled blood vessels

Increased mitoses and pleomorphism

Rhabdoid morphology

(a) Vimentin,
(b) desmin,
(c) cytokeratin

Cytology images

Contributed by Dr. Mark R. Wick

Embryonal, FNAB

Positive stains
Negative stains
Electron microscopy description
  • Skeletal differentiation, as evidenced by ultrastructural specific myofilament arrays, focal density, Z band material and pinocytotic vesicle, is suggestive of rhabdomyosarcomatous differentiation but is not specific for the diagnosis of rhabdomyosarcoma (J Pathol Transl Med 2015;49:93)
  • Features may not be evident in solid variants of the alveolar subtype
Molecular / cytogenetics description
  • Alveolar: t(2;13)(q35;q4), PAX3-FOXO1 fusion more frequent than t(1;13)(p36;q14), PAX7-POXO1 fusion
  • Embryonal: chromosome loss, deletion or uniparental disomy resulting in loss of chromosome 11 loci
  • Pleomorphic: complex karyotype
Differential diagnosis
  • Ewing sarcoma: strong membranous CD99 expression, myogenin negative, FLI1 nuclear expression and EWSR1 rearrangement in most cases
  • Heterologous rhabdomyosarcomatous differentiation in a malignant phyllodes tumor or in malignant peripheral nerve sheath tumor: extensive sampling to find diagnostic features of these tumor types
  • Invasive lobular carcinoma: keratin positive, desmin negative
  • Metastatic rhabdomyosarcoma: clinical history of primary rhabdomyosarcoma elsewhere
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