Malignant Fibrous Histiocytoma |
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Quick Review for Patients
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Malignant fibrous histiocytoma (MFH) was first described
in 1964 under the name malignant fibrous xanthoma.
Since that time several major variants have been identified and it has become
the most commonly diagnosed of all the sarcomas of adults.
Oral and maxillofacial sites are seldom involved, however, and the tumor
occurs primarily in the soft tissues of the extremities and
retroperitoneum.
Clinical Features
The MFH occurs primarily in adults, especially those 50-70 years of age, but rare cases have been described in children. Regardless of the histopathologic subtype, men are affected almost twice as frequently as women.
Within the maxillofacial region the most common complaint is a moderately
firm submucosal mass expanding slowly or moderately fast, with or without
pain and surface ulceration (Figure 1). The irregular nodular lesion
is typically unencapsulated and attached to surrounding tissues and adjacent
structures. It is usually less than 4 cm. in greatest diameter at the time
of biopsy. The myxoid variant often has quite a soft consistency and the
angiomatoid variant is often found in a location more superficial than that
of the other variants.
Pathology and Differential Diagnosis
MFH has a wide spectrum of cellular and tissue alterations. The cellular differentiation and density vary markedly, even within the same tumor. The classic histopathologic features, however, include at least mild cellular and nuclear pleomorphism, an admixture of fibroblastic and histiocytic elements, and focal areas with a storiform or cartwheel pattern of streaming spindle cells. This classic pattern is the one most frequently encountered in head and neck sites and is often referred to as the storiform-pleomorphic MFH (Figures 2 & 3).
Most lesional cells are spindled fibroblast-like cells which tend to be arranged in short woven fascicles or bundles with scattered areas showing a storiform pattern where fascicles intertwine. The spindle cells may be long and thin with minimal atypia, but there are usually areas with plump spindle cells containing enlarged, hyperchromatic and irregular nuclei (Figures 4 & 5). Varying numbers of rounded, polygonal and irregularly shaped histiocyte-like cells may dominate some areas of the lesion, often with very pleomorphic, multinucleated giant cells interspersed. The histiocytic cells have either abundant eosinophilic cytoplasm or pale foamy cytoplasm, and cell membranes are not easily visualized. Areas with histiocytic predominance usually have a haphazard structural appearance.
Chronic inflammatory cells are often scattered sparsely throughout the tumor, including foamy histiocytes, lymphocytes and plasma cells. Multinucleated Touton giant cells are occasionally seen. Mitotic activity varies widely and is directly related to the degree of cellular pleomorphism.
The fibrous stroma of MFH varies in density, being less pronounced in areas of lesser cellular differentiation. Myxoid stroma may be found and, rarely, foci of osteoid or cartilage metaplasia are present. While blood vessels are usually inconspicuous, some lesions present with numerous dilated, branching vessels. Depending on the dominant morphology, MFH is currently subclassified as one of several major variants: pleomorphic-storiform, myxoid, angiomatoid (aneurysmal), and giant cell MFH.
The myxoid variant is defined as a MFH with more than half of its stroma represented by myxoid change with spindle cells and scattered pleomorphic epithelioid cells (Figure 6). The vasculature is quite prominent and vessel walls appear thickened. To differentiate this tumor from myxoid liposarcoma, staining for hyaluronidase-sensitive mucopolysaccharides may be necessary. The liposarcoma, moreover, has a meshwork of thin-walled capillaries and tends to have a more uniform cellular histology with less spindling of lesional cells. The rare extraskeletal myxoid chondrosarcoma can be easily differentiated by its lack of stromal vascularity and structure, while the myxoid leiomyosarcoma almost always contains areas suggestive of smooth muscle differentiation.
The angiomatoid MFH has a prominent network of capillaries and arching veins with somewhat thickened walls and with plump endothelial nuclei (Figure 7). The vessels may be dilated to the point of appearing cystic, and stromal hemorrhage may be found. Myxoid stroma is seen in focal areas examples. Angiomatoid areas are interspersed with diffuse sheets of histiocytoid oval or spindled cells with minimal pleomorphism. Such cells are often concentrated around vascular channels and there may be occasional to moderate numbers of peripherally located lymphocytes. Lymphocytes also may be seen within the fibrous pseudoencapsulation of some lesions, sometimes associated with germinal centers. Multinucleated giant cells may demonstrate marked nuclear atypia.
The giant cell variant of MFH (giant cell tumor of soft tissue) is characterized by large numbers of osteoclast-like multinucleated giant cells scattered throughout a cellular stroma of histiocytoid and fibroblastic cells arranged in storiform nodules separated by fibrous septa (Figure 8). Stromal cells usually demonstrate moderate nuclear pleomorphism with occasional bizarre, hyperchromatic nuclei. A large proportion of cases show osteoid, even calcified bone, at the periphery.
The MFH often mimics the histopathologic appearance of other sarcomas, especially fibrosarcoma, pleomorphic liposarcoma, pleomorphic rhabdomyosarcoma, and hemangiopericytoma. Some lesions may , moreover, mimic benign fibrous histiocytoma or nodular fasciitis. The former is typically smaller, is more superficially located, and has much less cellular atypia, although mitotic activity might be abundant. The latter also has less cellular atypia and lacks evidence of peripheral invasion.
Fibrosarcoma may contain areas with a storiform pattern but it typically lacks significant pleomorphism and has no histiocytic or bizarre multinucleated giant cells. Pleomorphic liposarcoma may contain large numbers of pleomorphic giant cells, and fat stains may not help to distinguish between it and MFH because the histiocytic cells of the latter may contain lipids and the pleomorphic cells of the former may not contain lipids. The diagnosis of liposarcoma is aided considerably by the finding of signet-ring lipoblasts, especially when differentiating myxoid liposarcoma from myxoid MFH.
Pleomorphic rhabdomyosarcoma can be separated from MFH by the presence of cross-striations or longitudinal myofibrils in lesional cells. In the absence of these it may not be possible to differentiate these two malignancies without positive immunoreactivity with myogenic markers or the demonstration of rhabdomyoblasts by electron microscopy.
Hemangiopericytoma typically has a more uniform cell population than does
the angiomatoid variant of MFH. There is usually much less
cellular and nuclear pleomorphism and there is a pericellular network of
reticulin fibers demonstrated by silver reticulin stains.
Treatment and Prognosis
MFH of the oral region is usually treated by radical surgical resection, but at least 40% of lesions recur locally and a similar proportion metastasize within two years. Five-year survival is poor, no more than 30%, although it is somewhat better for the myxoid variant.
References (Chronologic Order)
Note: General references can be found by clicking on that topic to the left.
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