Stanford School of Medicine
Surgical Pathology Criteria
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Myxofibrosarcoma

Definition

  • Myxoid soft tissue neoplasm with cytologic pleomorphism

Alternate / Historical Names

  • Myxoid malignant fibrous histiocytoma

Diagnostic Criteria

  • Myxoid stroma must make up at least 10% of the tumor
  • Cellularity ranges from scattered cells to densely cellular foci
    • Cellular foci may resemble undifferentiated pleomorphic sarcoma (MFH)
  • Cytologic atypia and pleomorphism must be present at least focally
    • Enlarged hyperchromatic nuclei
    • Cytoplasmic acid mucin may simulate lipoblasts
    • Majority of cells may be bland in low grade lesions
  • Prominent curvilinear thin walled blood vessels
  • Multinodular growth pattern
  • Majority arise in dermis or superficial subcutaneous tissue
  • Usually involves extremeties or limb girdles
    • Rare on hands, feet, head, abdomen and retroperitoneum
  • The distinction from undifferentiated pleomorphic high grade sarcoma (MFH) is only relevant for low grade myxofibrosarcoma
    • Intermediate and high grade myxofibrosarcoma behaves as MFH
    • Thus the threshold for myxoid stroma (10 vs 50%) is not important
      • All low grade lesions must be overwhelmingly myxoid
    • See Grading/Staging at left sidebar
  • Robert V Rouse MD
    Department of Pathology
    Stanford University School of Medicine
    Stanford CA 94305-5342

    Original posting/last update: 7/16/11

Supplemental studies

Immunohistology

Vimentin positive
Smooth muscle actin occasional focal weak positive
S100 negative
CD34 occasional focal weak positive
MUC4 negative

Genetic analysis

  • No specific abnormality

 

Differential diagnosis

 

Myxofibrosarcoma Low Grade Fibromyxoid Sarcoma
Pleomorphic nuclei present At most, focal moderate pleomorphism, but usually minimal or absent
May be cellular Overall paucicellular
May have increased mitotic activity Few mitotic figures
Abnormal mitotic fibures may be present No abnormal mitotic figures
Lacks alternating fibrous and myxoid areas Features alternating fibrous and myxoid areas
Often subcutaneous Usually deep soft tissues

 

Myxofibrosarcoma High Grade Pleomorphic Sarcoma (MFH)
Prominent myxoid stroma Lacks myxoid stroma
Curvilinear vascular pattern No organized vascular pattern
  • Only high grade myxofibrosarcoma is in the differential diagnosis
    • No clinical significance to distinction in high grade cases

 

Myxofibrosarcoma Aggressive angiomyxoma
Large cytologically atypical cells Small bland cells
May have frequent mitotic figures Rare mitotic figures

 

Myxoid Liposarcoma Myxofibrosarcoma
Lipoblasts frequent No lipoblasts
Vacuoles in lipoblasts are clear Vacuoles, if present, contain material similar to adjacent myxoid stroma
Lacks pleomorphic cells At least focally pleomorphic
Rare in subcutis Frequent in subcutis
t(12;16) or t(12;22) No consistent abnormalities

 

Myxofibrosarcoma Intramuscular Myxoma and Juxta-articular Myxoma
Pleomorphism present Uniformly small bland cells
More cellular Extremely paucicellular
Mitotic figures may be present Mitotic figures practically never present
Arching vessels Markedly hypovascular

 

Myxofibrosarcoma Cellular Myxoma
Pleomorphism present Uniformly small bland cells
Mitotic figures may be present Mitotic figures rare
May have perivascular increase in cellularity No perivascular increase in cellularity

 

Fibromatosis, Abdominal Desmoid, Extra-abdominal Desmoid, Mesenteric, Retroperitoneal and Pelvic Myxofibrosarcoma
No pleomorphism Cytologic pleomorphism present
Usually dense stroma but focally may be myxoid No dense stroma
Vessels lack arching pattern Arching vessels

 

Myxofibrosarcoma Inflammatory Myxohyaline Tumor of Distal Extremities
Rare in distal extremities Distal extremities
May have frequent mitotic figures Infrequent mitotic figures
Infrequent inflammation Prominent inflammation

 

Myxoid DFSP Myxofibrosarcoma
No cytologic atypia or pleomorphism Atypical, pleomorphic nuclei
CD34 positive, nearly all cases Negative
No arcuate vascular pattern Arcuate vascular pattern

 

Myxofibrosarcoma Ischemic Fasciitis
Cytologically atypical to malignant No clear cytologic malignancy
Frequent atypical mitotic figures Atypical mitotic figures rare
Fat necrosis and fibrin rare Fat necrosis and fibrin characteristic
CD34 negative May be CD34 positive

 

Myxofibrosarcoma Giant Cell Fibroblastoma
Usually seen in adults, rare under 20 Mean age 3-6 years
Cytologically atypical but no multinucleated giant cells Giant cells appear multinucleated rather than cytologically atypical
May be mitotically active Mitotic figures rare
Lacks pseudovascular spaces Pseudovascular spaces present

Clinical

  • Age predominantly 50-80 years
    • Rare under 20
  • Recurrence rate 50-60%
    • Not related to grade
  • Metastatic rate related to grade
    • No metastases in low grade tumors
    • 20-35% metastasize in intermediate and high grade tumors
  • 5 year survival 60-70%

Grading/Staging/Report

Myxofibrosarcoma grading system (Mentzel 1996)

  • Low grade
    • Hypocellular, myxoid throughout
    • No solid areas
      • Atypical cells are scattered
    • No mitotic figures or necrosis
  • Intermediate grade
    • Myxoid throughout
      • May contain small solid areas
    • Increased cellularity, mitotic figures and pleomorphism
    • No necrosis or marked pleomorphism
  • High grade
    • Solid areas of pleomorphic sarcoma

French Federation of Cancer Centers System grading scheme for adult sarcomas

  • Tumor differentiation score = 2 for myxofibrosarcoma
  • Mitotic index
    • Score 1 0-9 mitoses per 10 hpf (0.1744 sq mm)
    • Score 2 10-19 mitoses per 10 hpf
    • Score 3 >19 mitoses per 10 hpf
  • Tumor cell necrosis
    • Score 0 No necrosis on any slide (one slide per 2 cm tumor diameter)
    • Score 1 <50% of tumor is necrotic on slides examined
    • Score 2 >50% of tumor is necrotic on slides examined
  • Final Grade (add the three scores above)
    • Grade 1 Sum of scores = 2 or 3
    • Grade 2 Sum of scores = 4 or 5
    • Grade 3 Sum of scores = 6 or more

Use TNM Staging

The surgical pathology report should contain or address the following:

  • Location
  • Type of resection or biopsy
  • Histologic diagnosis
  • Extent of tumor cell necrosis
  • Grade
  • Stage
  • Size
  • Depth (dermis, subcutis, below fascia, body cavity)
  • Margins
    • Involved
    • Not involved
      • If under 2 cm give all such distances and sites
      • If over 2 cm give minimum distance and site
  • Results of supplementary studies if performed
  • Relationship to other specimens from the same patient

 

Lists

Predominantly fibrous soft tissue sarcomas

Bibliography

  • Kempson RL, Fletcher CDM, Evans HL, Henrickson MR, Sibley RS. Tumors of the Soft Tissues, Atlas of Tumor Pathology, AFIP Third Series, Fascicle 30, 2001
  • Fletcher CDM, Unni KK, Mertens F. Pathology and Genetics of Tumours of Soft Tissue and Bone, World Health Organization Classification of Tumours 2002
  • Weiss SW, Goldblum JR. Enzinger and Weiss's Soft Tissue Tumors, 5th edition, 2008
  • Mentzel T, Calonje E, Wadden C, Camplejohn RS, Beham A, Smith MA, Fletcher CD. Myxofibrosarcoma. Clinicopathologic analysis of 75 cases with emphasis on the low-grade variant. Am J Surg Pathol. 1996 Apr;20(4):391-405.
 
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