Soft tissue

Fibroblastic / myofibroblastic



Topic Completed: 1 April 2013

Minor changes: 9 November 2021

Copyright: 2002-2022,, Inc.

PubMed Search: Myxofibrosarcoma [title] soft tissue

Annie S. Morrison, M.D.
Jerad M. Gardner, M.D.
Page views in 2021: 27,885
Page views in 2022 to date: 1,336
Cite this page: Morrison A. Myxofibrosarcoma. website. Accessed January 19th, 2022.
Definition / general
  • Spectrum of malignant fibroblastic lesions with myxoid stroma, pleomorphism and curvilinear vessels
  • A myxoid subtype of undifferentiated pleomorphic sarcoma (formerly myxoid malignant fibrous histiocytoma [MFH])
  • See also Heart chapter
  • Usually elderly patients, predominately in extremities, approximately 2/3 develop within the dermis and subcutis, remainder in deep skeletal muscle or other deep tissues (J Cutan Pathol 2008;35:935, Am J Dermatopathol 2003;25:281)
  • Retroperitoneal masses with similar histologic features are most likely dedifferentiated liposarcoma
Clinical features
  • 2/3 recur, 1/4 metastasize (lung, bone); better prognosis than other patterns of undifferentiated pleomorphic sarcoma
  • Local recurrences show increase in tumor grade and more complex karyotypes (Mod Pathol 2006;19:407)
Prognostic factors
Case reports
  • Wide local excision
  • Radiation therapy in select cases
  • Chemotherapy may be considered for metastatic disease
Gross description
  • Superficial tumors are multiple myxoid nodules, deep tumors are a single mass with infiltrative margins
  • High grade tumors often have tumor necrosis
Gross images

Images hosted on other servers:

Thigh tumor

Lower extremity tumor

Subcutaneous tumor

Microscopic (histologic) description
  • Multinodular tumor composed of pleomorphic spindle cells in myxoid background
  • "Pseudolipoblasts" may be seen (tumor cells with cytoplasmic vacuoles filled with mucin / myxoid material)
  • More solid areas are often seen similar to typical undifferentiated pleomorphic sarcoma
  • Curvilinear vessels (thick walled with broad arc) with condensation of cells around vessels is characteristic, incomplete fibrous septa, myxoid stroma (at least 10% of tumor) and infiltrating immature dendritic cells (Am J Clin Pathol 2003;119:540)
  • Has infiltrative periphery and often sends out long tentacles with frequent positive margins
  • High grade tumors are more cellular with atypical mitotic figures, hemorrhage, necrosis and possibly bizarre multinucleated giant cells
  • Rarely epithelioid

  • Controversial and contentious, various schemes exist
  • Grade does not predictive behavior (Hum Pathol 2004;35:612)
  • Low grade: minimal cellular atypia, 30%+ myxoid component, 20% or less solid component, 10% or less tumor necrosis
Microscopic (histologic) images

Contributed by Mark R. Wick, M.D.

Low grade, angervall tumor

High grade

Missing Image

Breast, high grade,
not myxofibrosarcoma
due to lack of

AFIP images

Myxoid areas may
have pleomorphic
cells and variable

Moderate cellularity with pleomorphic cells

Typical cellular areas with occasional giant cells

Grade I tumor has the minimal pleomorphism required for diagnosis

Grade II tumor: myxoid areas
alternate with solid area that is
not as pleomorphic as usual
undifferentiated pleomorphic sarcoma

Grade III tumor with markedly
pleomorphic areas (left) and
myxoid areas (right), myxoid
areas may lack pleomorphic cells

Resembling ischemic or proliferative fasciitis:

Myxoid stroma with low density of ganglion-like cells

Bizarre cells are strongly
suggestive of malignancy,
not a reactive condition

Not myxofibrosarcoma due to lack of pleomorphism:

These lesions are called juxta-articular myxoma, cellular intramuscular myxoma or myxoid lesion with recurrent potential, they may recur but do not metastasize (controversial lesions)

Images hosted on other servers:

Typical histology

Spindle shaped cells

Metastatic lesion of clavicle

Myxoid nodules and fibrous septa

Spindle shaped cells

Lipoblast-like cells

Curvilinear capillaries

Cytology description
  • Variable cellularity, myxoid granular to filamentous background in all cases, but less in high grade tumors
  • Tumor cells are round to spindled with variable shapes and sizes
  • Cytoplasm varies from scant to dense and tapering
  • Nuclei are large, pleomorphic and hyperchromatic, often with prominent nucleoli
  • Occasional multinucleated giant cells
  • High grade tumors resemble other adult pleomorphic sarcomas (Diagn Cytopathol 1999;20:6)
Positive stains
Negative stains
  • Fat stains (positive in cytoplasmic vacuoles of lipoblasts in liposarcoma but not in pseudolipoblasts), S100
Electron microscopy description
  • Fibroblastic differentiation in most cells; low grade tumors have spindled to plump cells with abundant cytoplasm, rich in well-developed rough endoplasmic reticulum cisternae, often distended and sometimes cystically dilated, containing electron lucent granular material, consistent with fibroblastic differentiation
  • Also cells with rough ER, well developed Golgi, lysosomes and filopodia, consistent with fibroblasts with histiocytic properties (Ultrastruct Pathol 2004;28:321)
Electron microscopy images

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Maxillary sinus tumor

Molecular / cytogenetics description
  • Highly complex karyotypes, often 6p-, 9q+, 12q+
Differential diagnosis
  • Low-grade fibromyxoid sarcoma: bland (usually not pleomorphic) spindle cells set in alternating myxoid and fibrous background, usually with whorled pattern and sometimes collagen rosettes (Histopathology 2004;45:29); lacks prominent curvilinear vascular structures and cellular atypia of myxofibrosarcoma
  • Myxoid liposarcoma: lipoblasts with clear cytoplasmic vacuoles, plexiform vasculature, monotonous nuclei usually with no pleomorphism or bizarre cells
  • Myxoma: no atypia, less prominent vasculature, no perivascular condensation of tumor cells, few mitotic figures, normal karyotype (J Cell Mol Med 2009;13:1291)
  • Nodular fasciitis: no atypical cells, no atypical mitotic figures
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