Soft tissue

Skeletal muscle


Spindle cell / sclerosing rhabdomyosarcoma

Editorial Board Member: Michael R. Clay, M.D.
Editor-in-Chief: Debra L. Zynger, M.D.
Erdener Özer, M.D., Ph.D.

Last author update: 1 May 2018
Last staff update: 2 November 2022 (update in progress)

Copyright: 2002-2023,, Inc.

PubMed Search: Sclerosing rhabdomyosarcoma

Erdener Özer, M.D., Ph.D.
Page views in 2022: 6,373
Page views in 2023 to date: 696
Cite this page: Özer E. Spindle cell / sclerosing rhabdomyosarcoma. website. Accessed January 30th, 2023.
Definition / general
Essential features
  • Spindle cell / sclerosing are considered the same diagnostic variant of rhabdomyosarcoma
  • Previously categorized as a part of embryonal rhabdomyosarcoma
Clinical features
Radiology images

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Large masticator space mass in neck

Cranial MRI

CT scan


Prognostic factors
  • In adults, recurrence and metastasis rate of 40 - 50% (Arch Pathol Lab Med 2015;139:1281)
  • In pediatric population, similar behavior to embryonal variant except parameningeal spindle cell is more aggressive (Arch Pathol Lab Med 2015;139:1281)
  • Prognosis of tumors in the head and neck is worse than those located in the extremities
Case reports
  • No consensus for optimal treatment
  • Mainstay therapeutic method should be similar to most soft tissue tumors including surgery and adjuvant chemotherapy or radiotherapy can be added (Int J Clin Exp Pathol 2015;8:13814)
Clinical images

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Cystic mass 10 × 10 × 8 cm

Gross description
  • Poorly circumscribed, fleshy, expanding masses
Microscopic (histologic) description
  • Neoplastic cells are arranged in lobules, small nests, microalveoli and single file arrays in an abundant hyalinized, eosinophilic to basophilic matrix that closely resembles primitive osteoid or chondroid material
  • Mitotic rate is very high (> 20 mitotic figures / 20 high power fields)
  • Spindle cells or small primitive-like cells embedded in abundant in collagen stroma
  • Scattered rhabdomyoblasts with eccentric nuclei and significant ample eosinophilic cytoplasm
  • In some cases tumor cells focally display a cribriform pattern closely mimicking adenoid cystic carcinoma
Microscopic (histologic) images

Contributed by Dr. Saroona Haroon, Case #457













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Hyalinizing collagenous matrix

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Neoplastic cells arranged into microalveoli

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Neoplastic cells arranged into lobules

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Hyalinized matrix resembles osteoid

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IHC positivity to desmin, myogenin, SMA, MyoD1

Spindle cell and sclerosing features

Uniformly distributed tumor cells

H&E, desmin, myogenin

Cytology images

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Fine needle aspiration

Positive stains
Negative stains
Electron microscopy description
  • Irregularly distributed disorganized filament in richly collagenized matrix
  • No Z bands
Molecular / cytogenetics description
Differential diagnosis
Board review style question #1
    Which of the following antibodies is strongly diffuse positive in sclerosing rhabdomyosarcoma?

  1. Actin
  2. CD99
  3. Desmin
  4. MyoD1
  5. Myogenin
Board review style answer #1
Board review style question #2
Which of the following is associated with sclerosing rhabdomyosarcoma?

A. PAX7-FOXO1A fusion
B. Polypoid growth with a cambium layer
C. Arises only in adults over 45
D. Pseudovascular growth pattern
Board review style answer #2
D. Sclerosing rhabdomyosarcomas often display a pseudovascular growth pattern. PAX7-FOXO1A fusion is associated with the alveolar subtype; polypoid growth with a cambium layer is seen in the botryoid type; and the pleomorphic subtype is seen in older patients.

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Reference: Spindle cell / sclerosing rhabdomyosarcoma
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