Primary malignant spindle cell sarcoma of bone
Most often malignant fibrous histiocytoma, but other pathologies include:
All are rare; they comprise less than 1% of all bone tumours. May arise in any bone (usually the metaphysis of a long bone) and tend to occur in middle age. Can occur after a previous insult to the bone, e.g. ionizing radiation, bone infarct, or fibrous dysplasia.
The treatment is surgical removal of all disease but, as with osteosarcoma, limb-sparing surgery and insertion of a customized prosthesis may be feasible. The role of chemotherapy is still being explored and comparison with historical controls does suggest some benefit.
Account for 5% of primary bone tumours and are usually benign. Occur in young adults, often in an epiphysis around the knee. Are treated by curettage and bone packing or bone resection and insertion of an endoprosthesis. Local recurrence occurs in 30-50%, but radiotherapy carries a definite risk of malignant transformation and is only appropriate where the alternative local therapy is amputation. Rarely, these tumours can metastasize to the lung. Where possible, these should be dealt with surgically. Anecdotal responses to chemotherapy have been reported.
Slow-growing tumours of middle to late age and the second most common bone tumour (approximately 20%). Occur around the pelvis and shoulders. Grade is a good guide to behaviour, although about 10% of low-grade tumours transform to a higher grade. Treatment is surgical resection with radiotherapy for incomplete resection or palliation of advanced disease.
Mesenchymal chondrosarcoma is a high-grade tumour of adolescence frequently involving the mandible, ribs, or spine. Combined treatment with surgery, chemotherapy, and radiotherapy provide a 50% cure rate.
Slow-growing tumour that arises from notochord remnant cells in the sacrum/coccyx (50%), skull base/clivus (35%), or upper cervical vertebrae, in middle age. Presents with persistent pain and often only discovered on CT or MRI after 'normal' plain X-rays of the bone. Metastases are rare (lung or bone) and survival is determined by the success or failure of local control.
Surgery is the treatment of choice but may not be feasible because of the tumour site. Radiotherapy (55-60 Gy) is used after incomplete resection or as palliation. Particle therapy with protons has shown some promise. 30-50% survive five years but late recurrences are possible.
Isolated lytic lesion rich in plasma cells. The diagnosis depends on the exclusion of myeloma (no other skeletal lesions, no hypercalcaemia, no suppression of other immunoglobulins, and bone marrow contains <5% plasma cells). Paraproteinaemia is common.
Treatment is either surgical excision of the lesion or, more commonly, radiotherapy (45-50 Gy). Prognosis is good, with a median survival of over 5 years, but about a half will transform into myeloma.
One of the differential diagnoses of malignant, small, round, dark cell tumours of bone (Ewing's neuroblastoma). Full staging with CT, bone scan, and bone marrow examination is required to exclude systemic lymphoma. Localized high-grade NHL is treated with initial chemotherapy (e.g. CHOP) followed by either radiotherapy or surgical excision and endoprosthesis (latter is preferred for long, weight-bearing bones, where there is otherwise a high risk of fracture). Multifocal disease is usually low-grade NHL. Treatment is with chlorambucil chemotherapy and radiotherapy.
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