Fibrous Histiocytoma of Bone: A Rare High-Grade Bone Sarcoma — Overview, Diagnosis & Treatment Options | MyMedicPlus

Malignant fibrous histiocytoma (MFH) of bone is a rare high-grade malignant bone tumor representing approximately 5% of primary malignant bone tumors and now classified under undifferentiated high-grade pleomorphic sarcoma of bone in the WHO 2020 classification. It predominantly affects adults aged 50-70 years, with a slight male predominance. The distal femur, proximal tibia, and humerus are the most common sites. Secondary MFH arising from prior radiation, Paget's disease, or bone infarct is well recognized.

Primary MFH of bone is sporadic in most cases, with no clear etiology. Secondary MFH of bone arises from pre-existing conditions: prior therapeutic radiation to bone (radiation-induced sarcoma, latency 5-30 years), Paget's disease of bone (approximately 1% develop sarcoma), bone infarct (avascular necrosis), prior orthopedic implants, chronic osteomyelitis, and fibrous dysplasia. No strong hereditary predisposition has been established. Complex chromosomal aberrations without a consistent specific translocation are characteristic.

Progressive bone pain, often worse at night, is the most common presenting symptom. A palpable soft tissue swelling or mass adjacent to the affected bone indicates cortical destruction and extraosseous extension. Pathological fracture through the tumor site occurs in approximately 20-30% of patients, particularly with Paget's disease-associated MFH. Restricted range of motion and joint effusion occur when the tumor is periarticular. Constitutional symptoms (fever, weight loss) are uncommon at presentation.

Plain radiograph shows an aggressive lytic bone lesion with poorly defined margins, cortical destruction, and soft tissue mass but without tumor bone formation. MRI with contrast delineates intramedullary extent, epiphyseal involvement, and neurovascular proximity. CT chest evaluates for pulmonary metastases (most common distant site). Technetium bone scan or PET-CT screens for skip lesions and distant bone metastases. Core needle biopsy (in the resection plane) provides tissue for diagnosis and exclusion of other high-grade bone sarcomas. MSTS/AJCC staging incorporates grade, compartment, and metastasis.

Treatment follows the high-grade osteosarcoma paradigm. Neoadjuvant chemotherapy (MAP: methotrexate, doxorubicin, cisplatin; or doxorubicin plus ifosfamide) for 2-4 cycles, followed by wide surgical resection (limb-salvage surgery with endoprosthetic reconstruction preferred, amputation if margins cannot be achieved), then adjuvant chemotherapy for 4-6 cycles based on histological response. Radiation therapy is used for unresectable or positive-margin cases. Pelvic and axial tumors require multidisciplinary surgical planning to achieve negative margins.

Five-year overall survival is approximately 30-50%, similar to high-grade osteosarcoma at the same stage. Histological response to neoadjuvant chemotherapy (greater than 90% tumor necrosis) is the strongest prognostic factor and predicts 5-year OS of approximately 60-70%. Pelvic and axial location, large tumor size, and pathological fracture adversely affect prognosis. Pulmonary metastases develop in approximately 50% of patients; surgical resection of isolated pulmonary metastases may be curative in selected cases.

No established prevention strategy exists for sporadic MFH of bone. Radiation dose and field should be minimized when treating other conditions to reduce radiation-induced secondary sarcoma risk. Patients with Paget's disease of bone should be informed of the approximately 1% risk of sarcomatous transformation and should seek evaluation promptly for new or worsening bone pain, particularly if a lytic lesion develops. Patients with prior radiation to bone require long-term surveillance for post-irradiation sarcoma.