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Malignant fibrous histiocytoma

Summary

Malignant Fibrous Histiocytoma (MFH) is a pleomorphic high grade tumor composed of fibroblasts, myofibroblasts, and histiocytes. MFH is the most frequent soft tissue tumor in adults. MFH is found in the lower extremity. Other less common sites include the retroperitoneum, and the head and neck.

The highest incidence is during the fifth decade of life and there is a male to female ratio of 1.5 to 1.
Clinically, MFH presents with local pain and swelling. There is often a history of a rapidly enlarging mass. Radiologically, MFH is an aggressive, permeative lesion which often lacks distinct features found in other high grade primary bone malignancies. It usually presents with a soft tissue mass with or without cortical erosion.
Complete Information on this Tumor
Introduction and Definition: 

Malignant Fibrous Histiocytoma (MFH) is a pleomorphic high grade tumor composed of fibroblasts, myofibroblasts, and histiocytes. MFH is the most frequent soft tissue tumor in adults. Primary osseus MFH is less common. MFH is found in the extremities 70-75% of the time and 50% of all cases are in the lower extremity1. Other less common sites include the retroperitoneum, and the head and neck. The highest incidence is during the fifth decade of life and there is a male to female ratio of 1.5 to 1.

Incidence and Demographics: 
MFH is secondary to another process such as radiation, surgery, fracture, osteonecrosis, Paget's disease, non-ossifying fibroma or fibrous dysplasia 20% of the time2. MFH arising from a previous abnormality is usually more aggressive and has a poorer prognosis than primary MFH. Primary osseus MFH is a central lesion found in the diaphysis or metaphysis of the bone that causes aggressive bone destruction and a soft tissue mass. The most common sites in order are the distal femur, proximal tibia, proximal femur and proximal humerus.
Symptoms and Presentation: 

Clinically, MFH presents with local pain and swelling. There is often a history of a rapidly enlarging mass. Pathologic fractures are present 20% of the time. Radiologically, MFH is an aggressive, permeative lesion which often lacks distinctive features found in other high grade primary bone malignancies. It usually presents with a soft tissue mass with or without cortical erosion. There is not normally a periosteal reaction.

X-Ray Appearance and Advanced Imaging Findings: 
Calcifications may be seen at the periphery of the mass on plain x-ray. On CT scan, the erosive, permeative destructive nature of the lesion is well seen, along with any soft tissue extension. CT scan is helpful in determining the extent of cortical erosion and intraosseus extension. MRI Findings in MFH are intermediate signal intensity on T1 weighted images and high intensity signal on T2 weighted images. MRI helps define the soft tissue mass, marrow involvement, neurovascular structures and joint invasion. MFH has increased uptake on bone scan which helps demonstrate any metastases.
Differential Diagnosis: 
The radiologic differential includes metastatic cancer, plasmacytoma, lymphoma, and fibrosarcoma.
Histopathology findings: 
On gross examination, MFH is a lobulated, fleshy, gray white mass. There may be yellow areas of lipid or darker areas of hemorrhage. The mass may be all soft tissue or have intraosseus extension. The margins of the tumor are normally ill-defined and destructive. Under the microscope there are five sub-types of MFH: storiformpleomorphic, myxoid, giant cell, inflammatory and angiomatoid. In all forms there are fibroblast and histiocyte elements in some ratio. The storiformpleomorphic form accounts for 50-60% of all MFH and is normally found in large muscle groups of the extremity. Plump spindle cells are found in a matted pattern in fascicles. A pinwheel pattern is found especially around vessels. They myxoid form is hypocellular and has a large mucoid component. The giant cell form has necrosis and hemorrhage in addition to giant cells. The inflammatory form has many inflammatory cells including xanthomas and is often found in the retroperitoneum. The angiomatoid form is often found in the subcutaneous tissues. MFH extends along fascial planes. Calcifications are formed by reactive periosteal cells and are not produced by tumor cells which helps to differentiate the tumor from fibrosarcoma. The cell of origin is still a matter of debate between a histiocyte and a mesenchymal cell. The tumor stains positive for histocytic markers CD68 and lysosome. Like other sarcomas, MFH is graded from 1 to 4 with a higher grade having a worse prognosis. Other tumors that must be excluded include myosarcoma and liposarcoma. MFH was introduced as a diagnosis in 1963 and prior to that time, tumors of this type were classified as rhabdomyosarcoma or fibrosarcoma. Some pathologists believe that many of the tumors now classified as MFH should be reclassified with a more specific diagnosis such as synovial cell sarcoma or leiomyosarcoma, based on careful study of cellular markers.
Treatment Options for this Tumor: 
Treatment of MFH depends on grade, stage and site. Patients may benefit from pre-operative chemotherapy before surgery. Chemotherapy may reduce the tumor bulk and increases the chances of a limb sparing procedure. Selective transcatheter intra-arterial chemotherapy has been employed to reduce systemic toxicity. Local recurrences are common.
Outcomes of Treatment and Prognosis: 
The prognosis of MFH becomes worse as a lesion is larger and deeper in the soft tissue. MFH metastasize to the lungs, lymph nodes, liver and bone.
Suggested Reading and Reference: 
1Murphey, MD et al., Musculoskeletal Malignant Fibrous Histiocytoma: Radiologic-Pathologic Correlation, RadioGraphics, 14:807826, July, 1994. 2Murphey, MD et al., Musculoskeletal Malignant Fibrous Histiocytoma: Radiologic-Pathologic Correlation, Radio Graphics, 14:807826, July, 1994. 3Murphey, MD et al., Musculoskeletal Malignant Fibrous Histiocytoma: Radiologic-Pathologic Correlation, Radio Graphics, 14:807826, July, 1994. Bullough, Peter, Orthopaedic Pathology (third edition), Time Mirror International Publishers Limited, London, 1997 Huvos, Andrew, Bone Tumors Diagnosis. Treatment and Prognosis, W.B. Saunders, Co., 1991.
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