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Contributors: Rajini Murthy MD, Erik Domingues MD, Nikki Levin MD, Susan Burgin MD
Other Resources UpToDate PubMed


Fibrosarcoma, also known as mesenchymal cell tumor or fibroblastic malignancy, is a rare tumor of malignant fibroblasts that usually occurs in the third to fifth decade of life. It generally presents as a painless, enlarging, poorly defined mass in the soft tissues. The lower extremities are a site of predilection, especially the thigh and knee, but the tumor can be found on the trunk, the upper extremities, and the head and neck. 

Fibrosarcomas usually arise deep to the subcutis, from fascia, including within muscle, or from aponeuroses or tendons. In this location, they may become attached to or encircle underlying bone. Very rarely, they may arise from the subcutaneous tissue. Trauma, chronic scarring, and prior irradiation have been implicated as causative factors. 

Many tumors that were previously classified as fibrosarcomas have recently been reclassified as other fibroblastic tumors. Therefore, prognostic data may not be reliable, and further contemporary studies are needed. After excision, local recurrence rates were reported to approach 60% but were reduced to 25% when postoperative radiation was used. The 5-year survival rate was reported to be 40%-60% in adults.

Metastases often arise within 2 years of diagnosis, but in histologically low-grade tumors, they may take many years to develop. The tumor metastasizes primarily to the lung and bone.

Related topic: infantile fibrosarcoma


C49.9 – Malignant neoplasm of connective and soft tissue, unspecified

443250000 – Malignant fibromatous neoplasm

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Diagnostic Pearls

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Differential Diagnosis & Pitfalls

  • Nodular fasciitis – Rapidly growing, painful mass presenting especially on the volar aspect of the forearm.
  • Myositis ossificans – Presence of metaplastic bone, many times following an episode of trauma.
  • Osteosarcoma – Produces tumor osteoid.
  • Desmoid tumor – Histology shows a relative increase in collagen and absence of cytologic atypia.
  • Monophasic synovial sarcoma – Histology may show focal calcifications, gland or gland-like spaces.
  • Malignant peripheral nerve sheath tumor – Arises from an identifiable nerve; apparent neurofibroma components may be present.
  • Liposarcoma – Histology shows lipocytes in well-differentiated tumors, or lipoblasts if less well-differentiated.
  • Malignant peripheral nerve sheath tumor (MPNST)
  • Undifferentiated pleomorphic sarcoma

Best Tests

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Last Reviewed:07/06/2021
Last Updated:07/06/2021
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A medical illustration showing key findings of Fibrosarcoma (Fibrosarcoma of Bone) : Bone pain, Pathologic fracture, Limited range of motion
Clinical image of Fibrosarcoma - imageId=984128. Click to open in gallery.
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