Soft tissue

Uncertain differentiation

Undifferentiated / unclassified sarcoma

Last author update: 1 August 2012
Last staff update: 20 January 2023 (update in progress)

Copyright: 2003-2023,, Inc.

PubMed Search: Undifferentiated / unclassified sarcoma

Vijay Shankar, M.D.
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Cite this page: Shankar V. Undifferentiated / unclassified sarcoma. website. Accessed February 8th, 2023.
Definition / general
  • Pleomorphic sarcoma composed of fibroblasts, myofibroblasts and histiocyte-like cells
  • Diagnosis of exclusion; must sample generously and search for other components to rule out a dedifferentiated tumor or evidence of specific differentiation other than fibroblasts or myofibroblasts
  • Previously called malignant fibrous histiocytoma (MFH), pleomorphic, myxoid or giant cell subtypes, but this terminology is no longer used
  • See also bone, eye-conjunctiva and heart-tumor chapters
  • First described in 1964 (Cancer 1964;17:1445)
  • Pleomorphic: variation in cytoplasmic and nuclear size throughout the tumor, not just funny looking cells
  • Historically considered the most common adult soft tissue sarcoma
  • Usually older adults (age 50+ years) with slight male predominance; more common in lower extremities, rarely retroperitoneum, head and neck, breast
  • Large and deep-seated with progressive enlargement
  • Sarcomas adjacent to orthopedic implants or postradiation are usually osteosarcoma or MFH (Mod Pathol 2001;14:969)
Case reports
  • Wide local excision is occasionally curative in extremities; adjuvant or neoadjuvant radiation and chemotherapy often used
  • Recurs locally, may metastasize to lungs or regional lymph nodes
  • Almost never presents as metastasis with unknown small primary
  • 5 year survival is 50 - 60% for all high grade pleomorphic sarcomas, better for some subtypes (dedifferentiated liposarcoma)
  • Call borderline if features are between fibrous histiocytoma and MFH, and treat with wide local excision
  • Good prognostic factors: superficial, small size, low grade
  • When occurs in skin, is difficult to differentiate from atypical fibroxanthoma or DFSP
Gross description
  • Large, may appear circumscribed (but is not); subcutaneous lesions are usually 5 cm or less, retroperitoneal lesions may be 20 cm
  • Cut surface is fibrous or fleshy with hemorrhage, necrosis or myxoid change
Gross images

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Sternal mass

Microscopic (histologic) description
  • Storiform pattern (cells emanate from a central focus), irregular fascicles, variable cellularity
  • Pleomorphic and bizarre tumor cells with foamy cytoplasm and marked atypia, in background of inflamed collagenous stroma
  • May represent end stage of various sarcomas with common morphologic features of pleomorphism and storiform growth pattern
  • Multinucleated giant cells may be seen; if prominent, classify as MFH-giant cell
  • Numerous mitotic figures, including atypical forms
  • Rarely metaplastic (not neoplastic) bone or cartilage
Microscopic (histologic) images

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AFIP images

Striking low power appearance
due to cellularity, whorled
pattern, marked pleomorphism
with bizarre nuclei

Tumor cells have abundant
eosinophilic cytoplasm
and bizarre nuclei and
resemble a muscle tumor

Characteristic giant cells with bizarre nuclei

Mixture of fibroblasts
and histiocyte-like
cells including
multinucleated forms

Vague storiform pattern is often present, at least focally

Strap like cells resemble rhabdomyoblasts

Numerous mitotic figures, some bizarre forms

Frequent tumor cell
necrosis, not seen
in benign fibrous

Osteoclast-like giant cells with uniform nuclei in a pleomorphic MFH

Tumor cells may form neoplastic bone and osteoid

Acute inflammatory cells and large histiocyte-like cells

Numerous histiocyte-like cells resembling lymphoma

Large histiocyte-like cells
with prominent nucleoli
resembling lymphoma or carcinoma,
with variable fibroblasts

Case #387

H&E images: low

H&E images: high








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Breast mass (recurrent)

Hard palate tumor (vimentin, CD68)

Hard palate tumor (H&E)

Cytology description
  • Single cells to large storiform fragments
  • Cells are spindled, plasmacytoid and pleomorphic (often multinucleated), all with malignant nuclear morphology (Cancer 1997;81:228)
Cytology images

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Various images

Positive stains
Negative stains
Electron microscopy description
  • No features of a specific lineage
  • Relatively undifferentiated fibroblastic, myofibroblastic or primitive mesenchymal cells, some with phagocytic properties
Molecular / cytogenetics description
Differential diagnosis
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