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
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
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
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 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
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
Recurrence rate 50-60%
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.
