Malignant fibrous histiocytoma: an ultrastructural perspective

Pathology of pleomorphic/undifferentiated and dedifferentiated bone neoplasms

Primary malignant bone tumors are uncommon and their accurate classification requires careful correlation of clinical, radiological, and pathologic findings. It is a heterogeneous group of tumors with a wide spectrum of morphology and their biological potential can be of low- or high-grade, depending on their risk for developing metastases. Over the past several decades, the classification of bone sarcomas has remained largely constant. However, some of the tumors have been reclassified and several new entities have emerged. In this review, we will focus on pleomorphic fibrosarcoma/UPS and dedifferentiated bone tumors, discuss their key diagnostic features, differential diagnosis, and their relation to prognosis.

Global protein-expression profiling for reclassification of malignant fibrous histiocytoma

According to the newest World Health Organization (WHO) classification for soft tissue tumors in 2013, malignant fibrous histiocytoma (MFH) has been gone. Most sarcomas called MFH were reclassified to be high-grade pleomorphic forms of leiomyosarcoma, liposarcoma, rhabdomyosarcoma, and other sarcomas by recent molecular technologies. However, about 10% to 15% of sarcomas called MFH before, still cannot be given a precise classification, and these are now called undifferentiated pleomorphic sarcoma or are still called MFH. Further molecular approaches including proteomic approaches are imperative to classify these unclassified sarcomas for improving clinical outcomes of the patients with soft tissue sarcomas. This article is part of a Special Issue entitled: Medical Proteomics.

Myxofibrosarcoma arising in the maxillary sinus: a case report with a review of the ultrastructural findings and differential diagnoses

This is a case report of a patient presenting with a destructive lesion with histologic features of a low grade malignancy in a predominantly myxoid matrix. Various low grade myxoid malignancies were considered in the differential diagnosis of which an overview is presented. A literature review of the ultrastructural findings and possible histogenesis is discussed along with the diagnostic criteria and recent change in the terminology regarding the malignancies previously diagnosed as myxoid malignant fibrous histiocytomas. A final diagnosis of a myxofibrosarcoma was only possible after assessing the immuno-histochemical profile, results of histochemical stains and ultrastructural features of this lesion.

Evidence for an unanticipated relationship between undifferentiated pleomorphic sarcoma and embryonal rhabdomyosarcoma

Embryonal rhabdomyosarcoma (eRMS) shows the most myodifferentiation among sarcomas, yet the precise cell of origin remains undefined. Using Ptch1, p53 and/or Rb1 conditional mouse models and controlling prenatal or postnatal myogenic cell of origin, we demonstrate that eRMS and undifferentiated pleomorphic sarcoma (UPS) lie in a continuum, with satellite cells predisposed to giving rise to UPS. Conversely, p53 loss in maturing myoblasts gives rise to eRMS, which have the highest myodifferentiation potential. Regardless of origin, Rb1 loss modifies tumor phenotype to mimic UPS. In human sarcomas that lack pathognomic chromosomal translocations, p53 loss of function is prevalent, whereas Shh or Rb1 alterations likely act primarily as modifiers. Thus, sarcoma phenotype is strongly influenced by cell of origin and mutational profile.

Undifferentiated high-grade pleomorphic sarcomas in children: a clinicopathologic study of 10 cases and review of literature

Undifferentiated high-grade pleomorphic sarcoma (UHGPS) is a sarcoma of debated nosology affecting adults, with rare cases reported in children. In order to investigate the clinicopathologic and prognostic features of pediatric UHGPS, 10 cases of UHGPS occurring before 18 years (mean age, 8.9 years) were analyzed. All were localized at diagnosis (head, 4; lower extremities, 4; trunk, 2), with a mean diameter of 4.5 cm. Mean follow-up was 6 years. Six patients were in complete remission, 1 after a relapse; 2 died of metastatic disease; 1 was alive with metastasis. Histologically, 8 tumors showed spindle cells with a focal or diffuse storiform pattern; 2 tumors had scattered aggregates of epithelioid cells. Two tumors displayed a prominent epithelioid component. Cellular pleomorphism, high mitotic rate with atypical mitoses, were found in all tumors; necrosis in 6 and vascular invasion in 2. CD68 and desmin were positive in 2 cases each, smooth muscle actin in 4, and S100 in 1. Five tumors in 1st and 1 in 2nd complete remission were superficial; 1 showed a spindle cell morphology with epithelioid foci, 3 had necrosis; 5 were grade 3; and 1 was grade 2. Three metastatic tumors (2 in the dura, 1 in the leg) displayed either a prominent epithelioid morphology (2) or scattered aggregates of epithelioid cells (1), with a myxoid background in 1. All were grade 3 and showed foci of necrosis. In summary, UHGPS is rare in children and frequently located in the head. A more favorable outcome is associated with superficial location. Foci of epithelioid cell may portend an aggressive behavior.

Pleomorphic Sarcoma as a Mimicker of Sarcomatous Carcinoma

The fourth case of a poorly differentiated sarcoma histologically mimicking a sarcomatous carcinoma is reported. The tumor was focally weakly positive for keratin, moderately focally positive for epithelial membrane antigen, muscle-specific actin, smooth muscle actin, and calponin, and strongly diffusely positive for vimentin. The neoplastic cells were closely apposed, often without intervening intercellular matrix; the cell membranes were straight and contained desmosome-like junctions. The cytoplasm contained a moderate number of mitochondria, rough endoplasmic reticulum, ribosomes, and many vesicles. The karyotype was complex and many chromosomal rearrangements were present. The diagnostic term carcinomatoid sarcoma is proposed for these interesting, insufficiently studies, tumors.

The Rise and Fall of Malignant Fibrous Histiocytoma

The term malignant fibrous histiocytoma was coined by Stout and associates in the 1960s to encompass pleomorphic soft tissue sarcomas presumably derived from histiocytes that are capable of fibroblastic transformation. The concept was reaffirmed in the following 2 decades and malignant fibrous histiocytoma thus was regarded as the most common soft tissue tumor in older adults. However, recent more critical clinicopathologic, ultrastructural, and immunohistochemical studies have shown that malignant fibrous histiocytomas are not derived from histiocytic "facultative fibroblasts" and many neoplasms so diagnosed actually are pleomorphic subtypes of other sarcomas. Meticulous electron microscopic and immunohistochemical investigations also found that the more common storiform-pleomorphic, myxoid, and perhaps the giant cell subtypes are composed of variable mixtures of fibroblasts and phenotypically modulated fibroblastic cells, notably myofibroblasts and histiofibroblasts. On the basis of these findings, we propose a new classification for the above subtypes of so-called malignant fibrous histiocytoma, the majority of which are variants of pleomorphic fibrosarcoma.

The Comparative Role of Immunohistochemistry and Electron Microscopy in the Identification of Myogenic Differentiation in Soft Tissue Pleomorphic Sarcomas

There is increasing evidence that histological classification of pleomorphic soft tissue sarcomas is prognostically useful, since a number of studies have provided evidence that myogenic differentiation is associated with a more aggressive clinical behavior. The aim of the current study was to analyze the role of electron microscopy in comparison with immunohistochemistry in the classification of soft tissue pleomorphic sarcomas. Thirty-nine pleomorphic sarcomas of the somatic soft tissues for which material for immunohistochemical and ultrastructural analysis was available were selected for this study. Cases were classified according to the criteria of the WHO classification of soft tissue tumors on the basis of the histologic appearance and of the results of immunohistochemical analysis, and then diagnoses were reconsidered at the light of the results of the ultrastructural analysis. The group of myogenic sarcomas included 13 leiomyosarcomas, 8 myofibrosarcomas, and 1 rhabdomyosarcoma, while the group of nonmyogenic sarcomas included 11 undifferentiated pleomorphic sarcomas/malignant fibrous histiocytomas (MFH), 4 myxofibrosarcomas, and 2 liposarcomas. Overall, there was a good concordance between immunohistochemistry and electron microscopy in recognizing myogenic differentiation in soft tissue pleomorphic sarcomas. Discrepancies included 1 case showing no immunoreactivity for muscle markers, which displayed ultrastructural features allowing reclassification as leiomyosarcoma, and 2 cases initially classified as undifferentiated pleomorphic sarcoma/MFH, which were reclassified as myofibrosarcomas after ultrastructural analysis. Ultrastructural analysis allowed the identification of pleomorphic sarcomas with myofibroblastic phenotype, a category that is not identifiable based on histologic and immunohistochemical profile. Notably, fibronexus junction was identified in tumor cells of 4 pleomorphic myofibrosarcomas, while 2 other lesions showed putative fibronexus junction structures, consisting of electron-dense straight fibrils adjacent to the cell surface, not clearly in continuity with cytoplasmic actin filaments. In conclusion, the results indicate that immunohistochemistry and electron microscopy can usefully complement each other in the classification of soft tissue pleomorphic sarcomas.

Malignant fibrous histiocytoma: between the past and the present

The precise nature and diagnostic concept of malignant fibrous histiocytoma (MFH) has been debated for years. Currently, a histiocytic lineage of the tumor cells is no longer favored. The nomenclature and classification of MFH and its subtypes have also been changed. The MFH pattern, especially that of storiform-pleomorphic variant, is viewed as a morphologic pattern shared by a number of sarcomas as well as by other nonsarcomas. Therefore, a diagnosis of MFH based solely on morphology is no longer acceptable and identification of a line of differentiation should be sought. A diagnosis of MFH should be made only for pleomorphic sarcomas in which no specific line of differentiation is discerned. Precise categorization of MFH-like tumors may require thorough sampling of the tumor and judicious use of immunohistochemistry and/or electron microscopy. Familiarity with the current terminology and classification of MFH and its subtypes is of paramount significance in the modern practice of pathology.

Undifferentiated pleomorphic sarcoma of the orbital region

Undifferentiated pleomorphic sarcoma (formerly known as malignant fibrous histiocytoma) has been established as an entity in the WHO-classification of soft tissue tumors since 2002. Before this the term "malignant fibrous histiocytoma" has been a collective term for soft tissue malignancies that had no distinct components and included most soft tissue sarcomas (40%). With the new classification they account for only about 5%, and tumors arising in the head and neck contribute only about 1-3% of all undifferentiated pleomorphic sarcomas. We report a rare case in which the orbital region was involved.

Das maligne fibr�se Histiozytom

The entity and nosology of pleomorphic malignant fibrous histiocytoma (MFH) is still ambiguous. The actual WHO-Classification uses pleomorphic malignant fibrous histiocytoma (MFH) and pleomorphic sarcoma NOS (not otherwise specified) synonymously. On the other hand text and illustrations convey the impression, that these tumors also could be pleomorphic lipo-, leio- or rhabdomyosarcomas etc. It would have been more informative to emphasize, that with the above mentioned specific sarcoma types MFH-like appearance may occur. Furthermore it would have been more up to date to consider pleomorphic sarcomas NOS as pleomorphic fibrosarcomas and include them in the chapter of fibroblastic and myofibroblastic tumors. This concept already has been carried out for the former myxoid variant of MFH, nowadays preferentially called myxofibrosarcoma. There is controversial discussion about the clinical significance of exact typing of pleomorphic sarcomas. Problems may also occur due to the lack of standards, which degree of desmin expression signifies leiomyosarcoma or just indicates myofibroblasts in MFH. The requirement of exclusion of other tumor-types before diagnosing pleomorphic fibrosarcoma still remains obligatory. After verification of the diagnosis pleomorphic sarcoma NOS or pleomorphic fibrosarcoma, grading e.g. according to criteria of the FFCCS can be carried out. Most cases of pleomorphic fibrosarcoma will qualify as high grade malignant.

Classification and subtype prediction of adult soft tissue sarcoma by functional genomics

Adult soft tissue sarcomas are a heterogeneous group of tumors, including well-described subtypes by histological and genotypic criteria, and pleomorphic tumors typically characterized by non-recurrent genetic aberrations and karyotypic heterogeneity. The latter pose a diagnostic challenge, even to experienced pathologists. We proposed that gene expression profiling in soft tissue sarcoma would identify a genomic-based classification scheme that is useful in diagnosis. RNA samples from 51 pathologically confirmed cases, representing nine different histological subtypes of adult soft tissue sarcoma, were examined using the Affymetrix U95A GeneChip. Statistical tests were performed on experimental groups identified by cluster analysis, to find discriminating genes that could subsequently be applied in a support vector machine algorithm. Synovial sarcomas, round-cell/myxoid liposarcomas, clear-cell sarcomas and gastrointestinal stromal tumors displayed remarkably distinct and homogenous gene expression profiles. Pleomorphic tumors were heterogeneous. Notably, a subset of malignant fibrous histiocytomas, a controversialhistological subtype, was identified as a distinct genomic group. The support vector machine algorithm supported a genomic basis for diagnosis, with both high sensitivity and specificity. In conclusion, we showed gene expression profiling to be useful in classification and diagnosis, providing insights into pathogenesis and pointing to potential new therapeutic targets of soft tissue sarcoma.

Omental malignant fibrous histiocytoma with a unique rough endoplasmic reticulum inclusion

The laminated inclusions in the rough endoplasmic reticulum (RER) are peculiar structures seen only in some cases of chondrocytes of pseudoachondroplasia. These ultrastructurally unique organelles have not yet been reported in inflammatory malignant fibrous histiocytoma (MFH). We describe an omental mass showing unique laminated inclusions in the RER in a young man with intra-abdominal inflammatory MFH. The most striking ultrastructural feature was a dilated RER containing a fine granular substance and a more electron-dense material exhibiting an onion skin-like lamellated or maze-like pattern, mimicking that of so-called laminated inclusions. These lamellated inclusions occupied most of the cytoplasm of the tumor cells. We speculate that the ultrastructural finding of the laminated RER inclusion is not specific for cartilage cells, but may represent abnormal accumulation of some kind of glycoprotein material or matrix protein. This granular material may undergo organization to form a peculiar laminated structure, probably due to a metabolic or fixation process. Further study is needed to elucidate the nature of this material.

Carcinosarcoma of the pancreas: a case report and review of the literature

We report the case of a 74-year-old white man with a mass in the head of the pancreas, which was found incidentally on computerized tomographic scan during a workup for deep vein thrombosis. Endoscopy with pancreatic duct brushings yielded a diagnosis of adenocarcinoma. A pancreaticoduodenectomy followed, with complete resection of the tumor. Pathologic examination showed 2 distinct components. One component was a conventional infiltrating pancreatic ductal adenocarcinoma, and the other component was high-grade sarcoma with features of malignant fibrous histiocytoma. To our knowledge, this carcinosarcoma is the seventh reported case of a primary pancreatic neoplasm with mixed carcinomatous and sarcomatous elements.