Malignant Fibrous Histiocytoma

Definition

  • Primary malignant neoplasm of bone & or soft tissue which contains fibrous & histiocytic elements

Epidemiology

  • Rare
  • 1 per million or one per 2 million
  • Affects older age group 40-70
  • More common in males

Site

  • Metaphysis of long bones, more so lower limbs than upper limbs

Aetiology

  • 20% arise secondary to other lesions such as fibrous dysplasia, bone infarction, Paget’s disease & irradiation

Pathology

  • “storiform pattern”
    • there is an appearance of wheel spokes radiating from a slit like vessel, in a fibrous background
    • A storiform pattern is not however diagnostic of MFH because it is also seen in osteosarcomas, leiomyosarcomas, neurogenic sarcomas, haemangiopericytomas & non ossifying fibromas
  • Other typical histological features are bizarre histiocytic cells, numerous mitotic figures, & scattering of chronic inflammatory cells

Histological variants:

  1. MFH – myxoid subtype
    1. Sheets of myxomatous tissue with large histiocytes & abnormal mitoses
  2. MFH – Inflammatory subtype
    1. Field of malignant histiocytes peppered with acute inflammatory cells, which may obscure the fibrous elements
  3. MFH – Giant cell type
    1. Large number of multinucleated giant cells
  • Stout’s hypothesis – theory of histiocytic & fibrous origin: histiocytes are derived from bone marrow monocytes – “tissue macrophages”. Histiocytes have the potential to transform to spindle cells which produce collagen, & are indistinguishable from fibrocytes
  • MFH is a diagnosis of exclusion; if the tumour resembles MFH but produces regions resembling another malignant tumour it is diagnosed as that tumour

Clinical

  • Pain, swelling, pathological fracture
  • Relatively high metastatic potential, usually to lungs & other bones

Investigations

Laboratory

No characteristic alterations

Xray

  • Lesions usually lytic or permeative; may expand cortex without breeching it
  • Frequent periosteal reaction
  • High index of suspicion if permeative radiolucency adjacent to bone infarct, fibrous dysplasia or Paget’s disease

MRI

  • T1 – low or intermediate intensity
  • T2 – high intensity

Immunohistochemistry

  • Vimentin stain positive
  • More specific is A1-AT antibody which also binds normal histiocytes

Treatment

  • Induction chemotherapy
  • Limb sparing surgery

Prognosis

  • Poor – around 60% 5ysr, but probably has a better prognosis than other sarcomatous lesions
  • Prognosis worse for secondary lesions. 40% alive at 4 years