Fibrosarcoma (Malignant Fibrous Histiocytoma)

Fibrosarcoma (Malignant Fibrous Histiocytoma)

G. Petur Nielsen, MD

Andrew E. Rosenberg, MD

AP radiograph of the distal femur reveals an eccentric lytic lesion of the metaphysis. It contains small fragments of residual bone engulfed by the tumor (sequestra). The margins are “moth-eaten.”

Fibrosarcoma of the distal femur appears as a variegated tan fleshy mass with pale yellow areas of necrosis and foci of hemorrhage. The tumor destroys the cortex and extends into the soft tissues.



  • Fibrosarcoma (FSA)


  • Pleomorphic malignant fibrous histiocytoma

  • Undifferentiated pleomorphic sarcoma

  • Fibroxanthosarcoma

  • Malignant fibrous xanthoma


  • High-grade sarcoma showing fibroblastic &/or myofibroblastic differentiation



  • In most tumors, there is no known predisposing factor

  • Approximately 20% of malignant fibrous histiocytomas arise in preexisting condition (secondary fibrosarcoma)

    • Paget disease

    • Patients with history of radiation to bone

    • Bone infarct

    • Diaphyseal medullary stenosis

  • Can also arise in association with prosthetic devices



  • Incidence

    • Rare tumor

    • Approximately 2% of primary malignant bone tumors

  • Age

    • Wide age group but usually affects middle-aged and elderly individuals

    • Most patients are > 50 years old at time of diagnosis

    • Rare cases occur in young individuals


  • Long bones

    • Most commonly femur followed by tibia and pelvis

    • Usually arises in metaphysis or diaphysis of long bones


  • Pain

  • Mass

  • Pathologic fracture


  • Treated like osteosarcoma of bone

    • Combination of chemotherapy and surgery ± radiation therapy


  • 5-year survival rate approximately 40-50%

  • Lung most common site for distant metastases


Radiographic Findings

  • Radiographic features are nonspecific and indicate an aggressive malignant neoplasm

  • Destructive

  • Lytic mass with “moth-eaten” pattern of destruction

    • Small sequestered fragments of residual bone may be present

  • Poorly circumscribed

  • Generally no sclerotic margin

    • If present, it is incomplete

  • Metaphyseal and usually eccentrically located

  • Cortical breakthrough and soft tissue mass commonplace

  • May be signs of preexisting lesion

MR Findings

  • Isointense to skeletal muscle on T1-weighted images

  • May show evidence of underlying lesion

CT Findings

  • Similar to radiographic findings

Bone Scan

  • Hot on bone scan


General Features

  • Variable gross appearance

  • Can be tan-white with areas of hemorrhage and necrosis

  • Involving medullary cavity and extending into adjacent soft tissue


  • Usually large at time of diagnosis


Histologic Features

  • Identical to soft tissue counterpart

    • Very diverse morphologic features with different patterns

    • Most common subtypes in bone are storiform pleomorphic type and giant cell-rich type

  • Fascicles of pleomorphic spindle-shaped cells arranged in a fascicular or storiform/pinwheel growth pattern

  • Multinucleated osteoclast-type giant cells are present in giant cell-rich type

  • Necrosis and a high mitotic rate, including presence of atypical mitotic figures, is common

  • Neoplastic cells often embedded within collagen-rich stroma that may be hyalinized

    • Often difficult to differentiate hyalinized collagen stroma from osteoid

  • Cells with epithelioid morphology, prominent vasculature with hemangiopericytoma-like growth pattern may also be present

  • Myxoid change commonly seen in myxofibrosarcoma of soft tissue, which is much less frequently encountered among intraosseous tumors

  • Rare cases of sclerosing epithelioid fibrosarcoma have been reported



  • Immunohistochemical findings in malignant fibrous histiocytoma are nonspecific and generally helpful in excluding other tumors in differential diagnosis

    • Neoplastic cells are diffusely positive for vimentin and may show focal staining for smooth muscle markers

      • Indicative of fibroblastic and myofibroblastic differentiation

    • Occasionally, tumor cells may show some keratin positivity, raising possibility of metastatic sarcomatoid carcinoma

  • Neoplastic cells can also stain for histiocytic markers

Electron Microscopy

  • Ultrastructurally, neoplastic cells usually show fibroblastic differentiation containing abundant intracytoplasmic rough endoplasmic reticulum

    • Some cells may contain myofibroblastic differentiation with peripheral filaments and densities

    • Some cells contain intracytoplasmic lysosomes (fibrohistiocytes)


High-Grade Osteosarcoma

  • Presence of extracellular collagen deposition in fibrosarcoma can sometimes be difficult to differentiate from neoplastic bone

  • Any mineralization of collagen fibers is suggestive of bone formation

  • Sometimes diagnosis of osteosarcoma does not become apparent until after resection when neoplastic bone is appreciated

  • Fortunately, both high-grade fibrosarcoma of bone and osteosarcoma are treated with osteosarcoma protocol and show similar response to chemotherapy

Dedifferentiated Chondrosarcoma

  • Dedifferentiated component in dedifferentiated chondrosarcoma is usually composed of undifferentiated pleomorphic sarcoma

  • Radiographic correlation is helpful in identifying underlying low-grade cartilaginous tumor

Metastatic Sarcomatoid Carcinoma

  • When high-grade fibrosarcoma is keratin positive, metastatic sarcomatoid carcinoma has to be excluded

  • Presence of single bone lesion favors primary bone tumor

  • In some cases, electron microscopy can be helpful


  • High-grade leiomyosarcoma can have similar histologic features

    • Neoplastic cells in leiomyosarcoma usually have more abundant eosinophilic cytoplasm

      • Stain for muscle markers such as desmin, muscle actin, and smooth muscle actin

      • Ultrastructurally, they show smooth muscle differentiation

Malignant Lymphoma

  • Can mimic fibrosarcoma radiographically

  • Easy to differentiate by light microscopy


  • Usually lytic and highly aggressive radiographically

  • Easy to distinguish histologically

    • Angiosarcoma stains for endothelial markers, which are negative in fibrosarcoma

Jul 6, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Fibrosarcoma (Malignant Fibrous Histiocytoma)

Full access? Get Clinical Tree

Get Clinical Tree app for offline access