Adult-Type Fibrosarcoma

 Most tumors classified as fibrosarcoma in older literature now reclassified as other entities


image Must lack features of well-defined fibrosarcoma subtypes and other entities

– Diagnosis of exclusion


image Lacks significant nuclear pleomorphism

– Tumors with marked pleomorphism classified as undifferentiated pleomorphic sarcoma




Clinical Issues




• Very rare if strictly defined [except for cases arising in dermatofibrosarcoma protuberans)

• Most arise in deep soft tissues of extremities in adults

• Treatment: Wide surgical resection

• Limited prognostic data using modern strict diagnostic criteria

• 50% overall mortality


Microscopic




• Uniform hyperchromatic spindle cells in herringbone fascicles

• Lacks characteristic features of other defined entities


Ancillary Tests




• Negative for keratin, EMA, S100, desmin, most others

• Lacks molecular signatures of other defined sarcomas


Top Differential Diagnoses




• Fibrosarcomatous dermatofibrosarcoma protuberans

• Undifferentiated pleomorphic sarcoma

• Synovial sarcoma

• Malignant peripheral nerve sheath tumor

• Desmoid fibromatosis

• Cellular dermatofibroma

• Low-grade myofibroblastic sarcoma

• Leiomyosarcoma

image
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.)


image
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.)

image
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 image.

image
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 image.


TERMINOLOGY


Definitions




• Sarcoma composed of spindle cells resembling fibroblasts
image Vast majority of tumors classified as fibrosarcoma in older literature now reclassified as other entities

image Currently, very rare entity, except for cases arising in dermatofibrosarcoma protuberans (DFSP)

image 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
image Very rare (if strictly defined)

– Most cases arise in DFSP in skin/superficial subcutis

• Age
image Median: 50 years


Presentation




• Usually deep mass of lower extremity but may occur anywhere
image Subset arise in subcutis


Treatment




• Wide surgical resection


Prognosis




• Only 2 modern studies using strict diagnostic criteria
image Most older series represent wide variety of sarcoma types (by current criteria); thus, unreliable data

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Apr 24, 2017 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Adult-Type Fibrosarcoma
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