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Soft tissue Tumors

Fibroblastic / myofibroblastic tumors

Fibrosarcoma of soft tissue - adult

Reviewer: Komal Arora, M.D. (see Reviewers page)
Revised: 12 November 2014, last major update July 2012
Copyright: (c) 2003-2014, PathologyOutlines.com, Inc.


● Malignant tumor of fibroblasts with herringbone architecture and variable collagen
● Rare (up to 3% of adult sarcomas)
● Some limit diagnosis to those age 10+ years, most patients are ages 40-55 years
● Many cases formerly called fibrosarcoma are actually dedifferentiated liposarcoma, fibromatosis, fibrosarcomatous DFSP, low-grade fibromyxoid sarcoma, MPNST, synovial sarcoma or MFH-pleomorphic
● Usually deep soft tissue of lower extremities or trunk, only rarely in retroperitoneum or mediastinum
● 50% recur, 25% metastasize (lung, bone)
● More metastases if more cellular and higher mitotic activity

● 5 year-41%, 10 year-29%
● Better if tumor is superficial and better differentiated, low mitotic rate, no necrosis

● See also peripheral ameloblastic fibrosarcoma, sclerosing epithelioid fibrosarcoma


● Radical excision, radiation if residual tumor or positive margins
● Possibly chemotherapy if high grade

Gross description

● May appear well circumscribed but nonencapsulated
● Fleshy, hemorrhagic, necrotic, white-tan

Gross images

Desmoid fibromatosis (left) is contrasted with high-grade fibrosarcoma (right), fibromatosis has gristle-like consistency, but fibrosarcoma tends to be white, fleshy and necrotic with an overlying tendon

Micro description

● Highly cellular fibroblastic proliferation in herringbone pattern (cells in columns of short parallel lines with all the lines in one column sloping one way and lines in adjacent columns sloping the other way)
● Cells have scant cytoplasm, tapering elongated dark nuclei with increased granular chromatin, variable nucleoli
● Mitotic activity present, often with abnormal forms
● Variable collagen
● Usually no giant cells
● No pleomorphism (or call pleomorphic MFH), no other distinct cell types

● Keloid-like (thick hyalinized collagen fibers), loose fascicular, focally myxoid

Micro images

Herringbone pattern

Atypical uniform cells in herringbone pattern

Cells are clearly malignant, with coarse chromatin but minimal pleomorphism

Grade I tumor has minimal pleomorphism and low mitotic index, but is more cellular than fibromatosis

Grade II tumor has intermediate features

Grade III tumor has high grade atypia and high mitotic index

Virtual slides


Positive stains

● Reticulin stain demonstrates fibers surrounding each cell
● Phosphotungstic acid-hematoxylin demonstrates abundant cytoplasmic fibrils
● Also vimentin, type 1 collagen, p53
● High Ki-67
● May be CD34+ if arises from DFSP or solitary fibrous tumor

Negative stains

● S100, keratin
● Smooth muscle markers, histiocytic markers, basal lamina

Electron microscopy description

● Fibroblasts with prominent rough endoplasmic reticulum but no myofilaments, no external lamina, no intercellular junction
● No distinct myofibroblasts (if present, call myofibrosarcoma)


● Aneuploid

Differential diagnosis

Other tumors with fibrosarcomatous areas:
● Dedifferentiated liposarcoma
● Fibromatosis: less cellular, less hyperchromasia, no atypia, < 1 mitotic figure/HPF
● Low grade fibromyxoid sarcoma
● MFH-pleomorphic
● Synovial sarcoma

Additional references


End of Soft Tissue Tumors > Fibroblastic / myofibroblastic > Fibrosarcoma of soft tissue - adult

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