Soft tissue
Fibroblastic / myofibroblastic tumors
Myxofibrosarcoma

Author: Annie S. Morrison, M.D. (see Authors page)
Editor: Jerad M. Gardner, M.D.

Revised: 26 August 2016, last major update April 2013

Copyright: (c) 2002-2016, PathologyOutlines.com, Inc.

PubMed Search: Myxofibrosarcoma [title] soft tissue

Cite this page: Myxofibrosarcoma. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/softtissuemyxofibrosarcoma.html. Accessed December 10th, 2016.
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
Epidemiology
  • 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
Treatment
  • 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

Micro 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

Grading:
  • 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
Micro Images

Images hosted on PathOut servers:

Low grade, angervall tumor, courtesy of Mark R. Wick, M.D.

High grade, courtesy of Mark R. Wick, M.D.



AFIP:

Myxoid areas may have pleomorphic cells and variable cellularity

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)

Missing Image

Breast, high grade, courtesy of Mark R. Wick, M.D.



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

Images hosted on other servers:

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