Undifferentiated pleomorphic sarcoma

Last author update: 1 November 2016
Last staff update: 29 December 2021

Copyright: 2002-2022,, Inc.

PubMed Search: Undifferentiated pleomorphic sarcoma [title]

Emily S. Reisenbichler, M.D.
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Cite this page: Reisenbichler ES. Undifferentiated pleomorphic sarcoma. website. Accessed July 5th, 2022.
Definition / general
  • See also Soft tissue topic
  • A malignant tumor showing no line of differentiation
  • Not part of the WHO classification of breast tumors
  • Previously known as malignant fibrous histiocytoma (MFH)
Essential features
  • High grade sarcoma with no distinctive microscopic, immunohistochemical or molecular features fitting any specific line of differentiation
  • Diagnosis of exclusion
  • Undifferentiated sarcomas account for approximately 20% of soft tissue sarcomas in other parts of the body but are exceedingly rare in the breast
  • May occur as a primary / de novo tumor or in the postradiation setting
Clinical features
  • Most occur in fifth to sixth decade of life
  • Majority present as rapidly enlarging palpable mass but can be incidental finding at screening
  • A limited core biopsy may underestimate tumor grade as grading systems such as the 3 tier French (FNCLCC) system are dependent on percentage necrosis and mitotic rate
Radiology description
Prognostic factors
  • Close / involved margins, large tumor size (> 5 cm) and high grade histology typically indicate a worse prognosis
Case reports
  • Surgical resection with a negative margin (R0) is standard treatment
  • Sentinel lymph node biopsy is not warranted
  • Adjuvant radiation is often utilized in large tumors or following incomplete (R1 / R2) surgical resections
  • Response to adjuvant chemotherapy is typically low but may be used in patients with large, unresectable or metastatic tumors
Clinical images

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Cystic tumor with skin tethering

Gross images

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Tumor invades skin

Specimen includes ribs posteriorly

Microscopic (histologic) description
  • Cell morphology may be spindle, round / epithelioid or pleomorphic, demonstrating marked cytologic atypia
  • Often high mitotic activity
  • May be associated with multinucleated giant cells or an inflammatory background
Microscopic (histologic) images

Contributed by Emily S. Reisenbichler, M.D. and Mark R. Wick M.D.
Missing Image

Spindle and epithelioid cells

Pleomorphic cells

Various images

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Marked nuclear pleomorphism and giant cells

Tumor necrosis
after neoadjuvant

Cytology description
  • Single or clustered spindled cells with nuclear pleomorphism
  • Absence of an epithelial component
Positive stains
Negative stains
  • Typically negative for most markers
Molecular / cytogenetics description
  • Complex karyotypes without specific recurrent aberrations
Differential diagnosis
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