Fibrosarcoma

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Tumor biology and incidence

  • Rare malignant spindle-cell neoplasm of mesenchymal origin
    • Accounts for fewer than 5% of bone sarcomas and 10% of all musculoskeletal sarcomas
  • Demonstrates fibroblastic differentiation and produces a collagen-rich fibrous tissue matrix
  • Spindle cells and matrix characteristically arranged as intersecting fascicles that form herringbone pattern
  • Differentiated from osteosarcoma by absence of osteoid production
  • Lacks the degree of pleomorphism and the bizarre cell typical of malignant fibrous histiocytoma of bone
  • At least 50% of tumors arise from metaphysis of distal femur or proximal tibia
  • Rarely, arises from surface of a bone; referred to as periosteal fibrosarcoma
  • May arise from underlying bone condition
    • Secondary to irradiation, Paget's disease, fibrous dysplasia, giant cell tumor, bone infarct, or chronic osteomyelitis
  • Multicentric lesions involving multiple bones rarely present at time of diagnosis

Age

  • Typically, patients older than age 50 years; however, wide range of ages has been observed, from children to older patients
  • Infantile form of fibrosarcoma exists (children <10yrs); has excellent prognosis when treated with adjuvant/neoadjuvant chemo and resection

Gender

M:F = 1:1

Presentation

  • Pain, localized tenderness and swelling
  • Restricted motion in the adjacent joint
  • Pathologic fracture (18% on initial presentation)

Plain films

  • Lesion usually purely lytic, permeative, or has a moth-eaten appearance
  • Arises eccentrically from metaphysis of bone extending into diaphysis
  • Cortical destruction and soft tissue extension usually evident
Site
  • Distal femur, proximal tibia, and pelvis
  • Few cases reported in humerus, scapula, hand, foot, radius, ribs, and spin
  • Location in bone: medullary versus periosteal, 2:1
Size
  • Variable
  • Usually larger than 5 cm
Tumor effect on bone
  • Lytic
  • Periosteal reaction, Codman's triangle, and hair-on-end patterns usually not present
  • No ossification or mineralization
Bone response to tumor
  • Permeative margin frequently observed
  • Sclerosis absent or scant
Matrix
  • Often totally radiolucent; no calcium or bone production
  • Dystrophic calcification may be seen
  • Background calcification/ossification of pre-existing lesion that has undergone sarcomatous degeneration may be present (such as bone infarct, Paget's disease)
Cortex
  • Cortical thinning and destruction
  • Periosteal reaction may be present; variable and generally less prominent than in osteosarcoma

Soft tissue mass

  • Commonly present
  • Can breach cortex and extend extraosseously into adjacent soft tissue
  • May also be seen as an isolated soft tissue lesion in the thigh or posterior knee arising deep to muscular fascia

Bone scan and chest CT

  • Nonspecific, but helpful in showing the extent of the lesion or the presence of additional sites of involvement
  • Necessary for systemic staging
  • Chest CT appropriate to rule out pulmonary metastases.

CT scan

  • Characterize extent of bony involvement, bone destruction, or bone reaction
  • Density of fibrosarcomas similar to that of surrounding normal muscle

MRI

Helps to define intraosseous spread and soft tissue extension or involvement of adjacent neurovascular structures

Differential diagnosis

  • Multiple myloma
  • Solitary metastasis
  • Malignant fibrous histiocytoma
  • Chondrosarcoma (dedifferentiated)
  • Ewing sarcoma (if less than 25 years old)
  • Giant cell tumor

Pathology

  • Gross: Tan to grayish white with rubbery consistency
  • Larger tumors may have myxoid, hemmorhagic, or necrotic foci
  • Microscopic: Varies with the level of differentiation
    • Well-differentiated, low-grade tumor
      • Homogeneous spindle-shaped fibroblasts with ovoid nuclei
      • Little pleomorphism
      • Infrequent mitoses
      • Prominent  herringbone pattern of fascicles of cells
    • Poorly differentiated, high-grade tumor
      • Pleomorphic cells
      • Abundant mitoses
      • Hyperchromic nuclei
      • Higher propensity for metastasizing early
  • Cellularity of tumor generally in inverse proportion to collagen production
  • IHC: Positive for vimentin, very weakly positive for smooth muscle actin
  • No definite etiology of fibrosarcoma known; genetic mutations likely play a role
  • Patients with multiple neurofibromas may have a 10% lifetime risk of developing fibrosarcoma

Diagnosis and treatment

  • Biopsy, in consultation with a musculoskeletal surgical oncologist
  • Tumor grade guides treatment regimen
    • Grade I tumor
      • Surgery, in many cases limb-sparing surgery (wide excision with reconstruction)
      • Survival rate: 80% at 10 years
    • Grade II tumor
      • Surgery plus adjuvant chemotherapy, although no definitive recommendations exist regarding chemotherapy for these intermediate-grade tumors
    • Grade III tumor
      • Induction chemotherapy, limb-sparing surgical resection, and postoperative chemotherapy. 
      • Overall 5-year survival rate ranges from 35% to 70%, depending on the study
  • Radiation usually administered only as a palliative measure for unresectable tumors or as a postoperative measure if margins were close or microscopically positive
  • Aggressive thoracotomy has been advocated for resection of pulmonary metastases (similar to treatment for osteosarcoma lung metastases)

Prognosis/outcome

  • Young age is favorable prognostic factor
    • According to Papagelopoulos et al, 5-year disease-free survival rate is 40% for patients 40 years or younger; only 12% for patients older than 40 years
  • Fibrosarcomas of bone carry worse prognosis than those of soft tissue
  • 15% local recurrence rate for surgically treated patients according to recent studies 
    • Univariate analysis of surgically treated patients: Age, location, grade, stage, surgical margins, and type of surgical procedure significantly affect disease-free survival and overall survival
  • Prognosis  most closely correlated with the grade of the tumor and presence of metastases at time of diagnosis
    • Patients with low-grade tumor have better survival rate than patients with a high-grade tumor
    • Overall survival rates at 5 years range from 28% to 34% for high-grade tumors and 50%-83% for low-grade tumors

Recommended reading

Papagelopoulos et al.  Primary Fibrosarcoma of Bone: Outcome after Primary Surgical Treatment.  CORR 2000 Apr;(373):88-103.

Wittig J. and Villalobos C.  Other Skeletal Sarcomas OKU 2 Musculoskeletal Tumors Ch19 pg 198-200.

Papagelopoulos et al.  Clinicopathologic Features, Diagnosis, and Treatment of Fibrosarcoma of Bone.  Am J Orthop 2002;31:253-257.

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