Histologically and genetically identical to conventional deep LGFMS
Clinical Issues
• Appear to represent 10-20% of reported cases of LGFMS
• Often adults (typically 3rd-4th decade), but wide range
Up to 1/3 arise in children and adolescents
• Most common in extremities (especially lower limb), buttock, and trunk
• Treatment: Complete surgical excision
• Better outcome reported than in deep forms of LGFMS
• Local recurrence uncommon; no metastases reported
Macroscopic
• Well-defined mass, most often in subcutis
• Median 4.2 cm (occasionally > 10 cm)
Microscopic
• Identical cytomorphologic features and spectrum as conventional LGFMS
• Variant morphology includes component of distinct collagen rosette-like structures
Ancillary Tests
• Diffuse MUC4(+) characteristic
• Rare focal or weak expression of CD34, EMA, or claudin-1
• Negative for keratins, S100, SMA, desmin
• Molecular: FUS rearrangements with CREB3L2 or CREB3L1
Top Differential Diagnoses
• Nodular fasciitis
• Fibromatosis
• Perineurioma
• Neurofibroma
• Cellular myxoma
• Dermatofibrosarcoma protuberans
• Myxofibrosarcoma
LGFMS Low-grade fibromyxoid sarcoma (LGFMS) is classically characterized by admixed fibrocollagenous and looser, myxoid zones. Most cases arise in deep locations, but a minority occur superficially in the subcutis or less likely dermis.
Collagenous Zones in LGFMS The collagenous zones of LGFMS tend to show relatively low cellularity, as depicted. On a limited biopsy, care must be taken to avoid misinterpretation as a benign process. Cytologically, the cells usually show mild to no atypia.
Myxoid Zones in LGFMS The myxoid zones of LGFMS are often more cellular than the fibrocollagenous zones and tend to feature a more prominent stromal vasculature, as depicted here.
Hyalinizing Rosette-Like Structures A distinctive morphologic variant of LGFMS contains a variable number of rosette-like structures with hyalinized collagenous cores . These tumors were originally described as hyalinizing spindle cell tumor with giant rosettes.
TERMINOLOGY
Abbreviations
• Low-grade fibromyxoid sarcoma (LGFMS)
Synonyms
• Evan tumor
• Hyalinizing spindle cell tumor with giant rosettes
• Fibrosarcoma, fibromyxoid type
Definitions
• Subset of low-grade fibromyxoid sarcoma arising in dermis &/or subcutaneous tissue
Histologically and genetically identical to conventional deep LGFMS
CLINICAL ISSUES
Epidemiology
• Incidence
Appear to represent 10-20% of reported cases of LGFMS
Probably underreported in literature
• Age
Often adults (typically 3rd-4th decade) but wide range
– Up to 1/3 arise in children and adolescents
• Sex
M > F
Site
• Most common in extremities (especially lower limb), buttock, and trunk
• Occasionally other sites
Presentation
• Usually slow-growing, painless mass
Treatment
• Complete surgical excision
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and looser, myxoid 
zones. Most cases arise in deep locations, but a minority occur superficially in the subcutis or less likely dermis.
. These tumors were originally described as hyalinizing spindle cell tumor with giant rosettes.
