Myxofibrosarcoma

Definition

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