Soft tissue

Skeletal muscle

Rhabdomyosarcoma

Pleomorphic rhabdomyosarcoma


Editorial Board Member: Nasir Ud Din, M.B.B.S.
Deputy Editor-in-Chief: Borislav A. Alexiev, M.D.
Erica Kao, M.D.
Cecilia Belzarena, M.D, M.P.H.

Last author update: 6 September 2022
Last staff update: 6 September 2022

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PubMed Search: Pleomorphic rhabdomyosarcoma

Erica Kao, M.D.
Cecilia Belzarena, M.D, M.P.H.
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Cite this page: Kao E, Belzarena C. Pleomorphic rhabdomyosarcoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/softtissuepleomorphicrhabdo.html. Accessed February 3rd, 2023.
Definition / general
  • High grade pleomorphic sarcoma composed of bizarre eosinophilic, round and spindle cells with skeletal muscle differentiation
  • Exceedingly rare category of rhabdomyosarcoma (RMS) in adults
  • Highly aggressive tumor associated with poor prognosis (Anticancer Res 2015;35:6213)
Essential features
  • High grade sarcoma composed of atypical cells that display skeletal muscle differentiation, confirmed with immunohistochemistry for myogenin or myoD1
Terminology
  • Pleomorphic rhabdomyosarcoma
ICD coding
  • ICD-O: 8901/3 - pleomorphic rhabdomyosarcoma, NOS
  • ICD-11: 2B55 & XH5SX9 - rhabdomyosarcoma, primary site & pleomorphic rhabdomyosarcoma, NOS
Epidemiology
Sites
Pathophysiology
  • Complex karyotype but no signature genetic alteration
Etiology
  • Unknown
Clinical features
  • Rapidly growing, painful deep mass, most commonly of lower extremity
  • Nodal involvement uncommon (< 10%)
  • Majority of patients (70%) with localized disease at presentation (Anticancer Res 2015;35:6213)
Diagnosis
  • Pleomorphic cells with brightly eosinophilic cytoplasm (Mod Pathol 2001;14:595)
  • Skeletal muscle differentiation as confirmed by desmin, myogenin or MyoD1 (Ann Diagn Pathol 2018;36:50)
  • Thorough histologic sampling and evaluation are necessary for diagnostic confirmation
Radiology description
  • In MRI T1 weighted sequences, the tumor appears iso or hypointense to muscle
  • In T2 weighted and STIR sequences, the tumor is hyperintense with surrounding edema
  • In postcontrast sequences, the mass shows heterogeneous enhancement; necrosis is usually present within
  • Reference: AJR Am J Roentgenol 2007;189:371
Radiology images

Contributed by Erdener Özer, M.D., Ph.D.
MRI

MRI



Images hosted on other servers:
MRI

MRI

Adductor brevis

Adductor brevis

Prognostic factors
  • High propensity for metastatic spread
  • Lungs are the most common site for metastases (77%)
  • Positive margins associated with disease relapse (Anticancer Res 2015;35:6213)
  • Tumors with superficial location (~20%) have a more favorable outcome
Case reports
Treatment
  • Clinical behavior and responsiveness to chemotherapy are similar to adult high grade soft tissue sarcomas
  • Poor prognosis with median survival of 7 months
  • Surgical resection with wide margins is mainstay of treatment
  • Stereotactic body radiation therapy (SBRT) has been used for lung oligometastases (Cancer Treat Res Commun 2021;26:100282)
Gross description
Gross images

Contributed by Debra Zynger, M.D.

Seemingly circumscribed thigh mass

Variable hemorrhage

Variable necrosis



Images hosted on other servers:

Paratesticular tumors

Resected tumor

Microscopic (histologic) description
  • Sheets of large, atypical and frequently multinucleated polygonal, spindled or rhabdoid eosinophilic cells (Am J Surg Pathol 2009;33:1850)
  • Cross striations are seldom detected
Microscopic (histologic) images

Contributed by Burcin Tuna, M.D. and AFIP images

Bizarre, eosinophilic multinucleated cells

Rhabdomyoblasts

Fascicular pattern

Storiform pattern


Patternless pattern

Spindle cells

Pleomorphic and polygonal cells

Epithelioid cells with abundant eosinophilic cytoplasm

Desmin

MyoD1

Positive stains
Electron microscopy description
  • Skeletal muscle differentiation with rudimentary sarcomeres containing Z bands or Z band material with thick and thin filaments (Mod Pathol 2001;14:595)
Molecular / cytogenetics description
Sample pathology report
  • Soft tissue, biopsy:
    • Pleomorphic sarcoma with rhabdomyoblastic differentiation (see comment)
    • Comment: These findings may represent a pleomorphic rhabdomyosarcoma, although heterologous differentiation cannot be excluded.
Differential diagnosis
  • Embryonal or alveolar rhabdomyosarcoma with anaplastic features:
    • No evidence of embryonal or alveolar component which may have scattered pleomorphic cells or solid foci of pleomorphic cells (Am J Surg Pathol 1993;17:601)
      • Embryonal RMS has ovoid to spindle cells, typically occurs in the pediatric population but can be in adults, and has a predilection for the head and neck and genitourinary system (Pediatr Blood Cancer 2021;68:e28798)
    • Alveolar RMS tumor cells are arranged in nests separated by fibrovascular septa, which frequently exhibit loss of cellular cohesion in the center, conferring a pattern of irregular alveolar spaces; the presence of either a PAX3::FOXO1 or a PAX7::FOXO1 fusion gene is detected in the majority of alveolar RMS cases
    • Pleomorphic RMS prefers older adults and occurs in the extremities (Am J Surg Pathol 2009;33:1850)
  • Undifferentiated pleomorphic sarcoma:
    • Diagnosis of exclusion
    • No evidence of skeletal muscle differentiation
  • Pleomorphic liposarcoma:
    • No evidence of skeletal muscle differentiation
  • Carcinomas with rhabdomyosarcomatous differentiation, such as malignant mixed Müllerian tumor:
    • Carcinomatous component present
  • Melanoma with rhabdomyosarcomatous dedifferentiation (Am J Surg Pathol 2016;40:181):
    • Presence of BRAF mutation, history of melanoma with current presentation of tumor in a characteristic site of metastasis (lymph node, lung, etc.)
  • Sarcomas with heterologous rhabdomyoblastic differentiation, such as dedifferentiated liposarcoma or MPNST (malignant Triton tumor):
    • Histologic or molecular evidence of another tumor (i.e., MDM2 amplification present for dedifferentiated liposarcoma or a well differentiated liposarcoma component present), loss of H3K27me3 in MPNST or areas of more classic appearing MPNST arising from a nerve
Board review style question #1

Which of the following is true for pleomorphic rhabdomyosarcoma?

  1. A t(2;13)(q36;q14) translocation is found in the majority of alveolar rhabdomyosarcoma
  2. Composed of an embryonal component
  3. May express pankeratin
  4. Tumor cells often display cross striations
  5. Usually are tumors of children
Board review style answer #1
A. A t(2;13)(q36;q14) translocation is found in the majority of alveolar rhabdomyosarcoma

Comment Here

Reference: Pleomorphic rhabdomyosarcoma
Board review style question #2
Which rhabdomyosarcoma type is more predominant in adults in the sixth to seventh decades and is characterized by the presence of pleomorphic cells with a significant amount of bright eosinophilic cytoplasm?

  1. Alveolar rhabdomyosarcoma
  2. Embryonal rhabdomyosarcoma
  3. Pleomorphic rhabdomyosarcoma
  4. Spindle cell / sclerosing rhabdomyosarcoma
Board review style answer #2
C. Pleomorphic rhabdomyosarcoma

Comment Here

Reference: Pleomorphic rhabdomyosarcoma
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