Surgical Pathology Criteria–

Low Grade Fibromyxoid Sarcoma

Differential Diagnosis

Extra-abdominal Desmoid Fibromatosis Low Grade Fibromyxoid Sarcoma
Nuclei may be vesicular Small dark nuclei
Sweeping bundles of cells Swirling, whorled pattern
No rosettes May have collagenous rosettes
Frequent slit-like vessels No slit-like vessels

 

Low Grade Myxofibrosarcoma Low Grade Fibromyxoid Sarcoma
Pleomorphic nuclei present At most, focal moderate pleomorphism, but usually minimal or absent
May be cellular Overall paucicellular
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 deef soft tissues

 

Aggressive Angiomyxoma Low Grade Fibromyxoid Sarcoma
Unifiorm myxoid pattern Alternating fibrous and myxoid patterns
Prominent large vessels No prominent large vessels
Restricted to pelvis, perineum, genitalia Frequently occurs in other sites
Desmin positive Usually desmin negative

 

Low Grade Fibromyxoid Sarcoma Intramuscular Myxoma
Alternating fibrous and myxoid patterns Uniform myxoid pattern
Swirling, whorled pattern No swirling, whorled pattern

 

Low Grade Fibromyxoid Sarcoma Juxta-articular Myxoma
Alternating fibrous and myxoid patterns Uniform myxoid pattern
Swirling, whorled pattern No swirling, whorled pattern

 

Low Grade Fibromyxoid Sarcoma Cellular Myxoma
Alternating fibrous and myxoid patterns Uniform myxoid pattern
Swirling, whorled pattern No swirling, whorled pattern

 

Neurofibroma Low Grade Fibromyxoid Sarcoma
May have thick collagen bundles Lacks thick collagen bundles
S100 positive S100 rare to negative, except may be positive around rosettes
No rosettes May have collagenous rosettes

 

Spindle Cell Atypical Lipomatous Tumor Low Grade Fibromyxoid Sarcoma
Adult fat integral to lesion No fat component
Lipoblasts may be present No lipoblasts
Abnormal mitotic fibures may be present No abnormal mitotic figures
Areas may be histologically identical

 

Low Grade Fibromyxoid Sarcoma Sclerosing Epithelioid Fibrosarcoma
Alternating fibrous and myxoid areas Generally myxoid stroma
Spindled or stellate cells Round, oval or angulated cells
EMA occasionally weak or focal EMA positive in 50% of cases
Quite different in appearance but based on cases with shared t(7;16) and cases with shared histologic features it has been suggested that these represent ends of a common spectrum

 

Soft Tissue Perineurioma Low Grade Fibromyxoid Sarcoma
Fibrous capsule Grossly circumscribed but microscopically infiltrating
Alternating pattern not prominent Alternating fibrous and myxoid stroma
Myxoid areas infrequent Myxoid areas definitional
EMA 100% positive EMA occasional focal weak positive

 

Myxoid DFSP Low Grade Fibromyxoid Sarcoma
Superficial Usually deep soft tissues
CD34 positive, nearly all cases Only occasional weak positivity
Usually more cellular Generally hypocellular, at most focally hypercellular

 

Nodular Fasciitis Low Grade Fibromyxoid Sarcoma
Usually superficial Usually deep soft tissues
S and C shaped bundleslll of cells Alternating fibrous and myxoid areas with whorling
Small Usually large
Essentially never metastasizes Metastatic rate reported from 6-60%, probably closer to 10%
LGFS may contain areas indistinguishable from nodular fasciitis; both are composed of bland cells

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