Adult-Type FS The rare adult-type fibrosarcoma (FS) should be diagnosed only after all morphologically similar entities have been rigorously excluded. Strictly defined cases demonstrate prominent fascicular growth by spindled tumor cells lacking significant nuclear pleomorphism. (Courtesy K. Fritchie, MD.)
Fascicular Herringbone Pattern in FS Relatively uniform spindle cells are arranged in prominent fascicles that intersect at acute angles giving rise to the characteristic herringbone pattern. (Courtesy K. Fritchie, MD.)
FS Arising in Dermatofibrosarcoma Protuberans This is an example of FS arising in a dermatofibrosarcoma protuberans (DFSP), the most common scenario in which FS is seen in the skin/subcutaneous tissue. Note the background of honeycombing fat entrapment, typical of DFSP .
Higher Magnification of FS Arising in Dermatofibrosarcoma Protuberans Higher magnification of a cellular area of FS arising in DFSP shows significant nuclear atypia, pleomorphism, and multiple mitotic figures .
TERMINOLOGY
Definitions
• Sarcoma composed of spindle cells resembling fibroblasts
Vast majority of tumors classified as fibrosarcoma in older literature now reclassified as other entities
Currently, very rare entity, except for cases arising in dermatofibrosarcoma protuberans (DFSP)
Diagnosis should only be made with extreme caution
• Lacks features of well-defined fibrosarcoma subtypes
• Pleomorphic high-grade fibroblastic sarcomas are currently classified as undifferentiated pleomorphic sarcoma (PS)
CLINICAL ISSUES
Epidemiology
• Incidence
Very rare (if strictly defined)
– Most cases arise in DFSP in skin/superficial subcutis
• Age
Median: 50 years
Presentation
• Usually deep mass of lower extremity but may occur anywhere
Subset arise in subcutis
Treatment
• Wide surgical resection
Prognosis
• Only 2 modern studies using strict diagnostic criteria
Most older series represent wide variety of sarcoma types (by current criteria); thus, unreliable data
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