Breast malignant, males, children
Undifferentiated pleomorphic sarcoma (UPS)

Author: Emily S. Reisenbichler, M.D.

Revised: 15 October 2018, last major update November 2016

Copyright: (c) 2002-2018,, Inc.

PubMed Search: Undifferentiated pleomorphic sarcoma [title]

Cite this page: Reisenbichler, E.S. Undifferentiated pleomorphic sarcoma (UPS). website. Accessed October 24th, 2018.
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
Images hosted on other servers:

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
Images hosted on PathOut server:

Contributed by
Emily S. Reisenbichler, M.D.

Missing Image

Various images

 Contributed by
 Mark R. Wick M.D.

Various images

Images hosted on other servers:

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