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.

Fibrohistiocytic skin tumors

The fibrohistiocytic tumors of the skin are a heterogeneous group of dermal/subcutaneous mesenchymal neoplasms which show fibroblastic, myofibroblastic and histiocytic (macrophage-like) differentiation, often one beside the other in the same tumor. "Fibrohistiocytic" means in this context the morphologic similarity of the cells with fibroblasts and histiocytes. The WHO classification of 2005 includes the following entities as fibrohistiocytic tumors of the skin: BENIGN: 1. Fibrous histiocytoma (FH)/(synonymous: Dermatofibroma. Variants of FH: 1a. cellular fibrous histiocytoma, 1b. atypical (pseudosarcomatous) fibrous histiocytoma, 1c. aneurysmatic fibrous histiocytoma, 1d. epithelioid fibrous histiocytoma; 2. dermatomyofibroma; 3. (juvenile) xanthogranuloma. INTERMEDIATE: 4. plexiform fibrohistiocytic tumor; 5. dermatofibrosarcoma protuberans; 6. atypical Fibroxanthoma. MALIGNANT: 7. malignant fibrous histiocytoma. All these entities are reviewed in this paper with particular attention devoted to differential diagnostic considerations.

High Proliferative Activity Excludes Dermatofibroma: Report of the Utility of MIB-1 in the Differential Diagnosis of Selected Fibrohistiocytic Tumors

Context.—Dermatofibroma is a benign fibrohistiocytic tumor composed of a mixture of fibroblastic and histiocytic cells. The diagnosis of this tumor is generally uncomplicated; however, rare variants may be difficult to distinguish from malignant fibrohistiocytic tumors. Deep penetrating dermatofibroma may be difficult to distinguish from dermatofibrosarcoma protuberans, and pseudosarcomatous dermatofibroma and dermatofibroma with monster giant cells share morphologic similarities with malignant fibrous histiocytoma and atypical fibroxanthoma.

Objective.—To find an immunohistochemical marker or markers that differentiate between fibrohistiocytic lesions of skin.

Design.—We evaluated the immunophenotypic characteristics of 83 fibrohistiocytic tumors (36 typical dermatofibromas, 16 cases of dermatofibrosarcoma protuberans, 16 malignant fibrous histiocytomas, and 15 atypical fibroxanthomas) using antibodies against MIB-1 (Ki-67), factor XIIIa, CD34 (HPCA-1), HHF35 (muscle-specific actin), 1A4 (smooth muscle actin), cytokeratin (AE1/AE3, CAM 5.2, and 34βE12), S100 protein, and desmin.

Results.—A high proliferative index detected by MIB-1 staining excluded the possibility of dermatofibroma and was diagnostically useful in separating this entity from dermatofibrosarcoma protuberans, malignant fibrous histiocytoma, and atypical fibroxanthoma. A low proliferative index, however, could not differentiate dermatofibroma from dermatofibrosarcoma protuberans. Factor XIIIa reactivity was not helpful for the diagnosis of dermatofibroma, whereas CD34 reactivity was statistically significant in the diagnosis of dermatofibrosarcoma protuberans. The sensitivity of these 2 markers is low and therefore of questionable practical diagnostic value.

Conclusion.—Evaluation of the proliferative index may further assist in distinguishing dermatofibroma from dermatofibrosarcoma protuberans, atypical fibroxanthoma, and malignant fibrous histiocytoma.

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.

Malignant fibrous histiocytoma of soft tissue: an abandoned diagnosis

Malignant fibrous histiocytoma (MFH) has been regarded as the most common soft-tissue sarcoma of adult life. Since it was first recognized in the early 1960s, however, MFH has been plagued by controversy in terms of both its histogenesis and its validity as a clinicopathologic entity. The latest World Health Organization classification no longer includes MFH as a distinct diagnostic category but rather as subtypes of an undifferentiated pleomorphic sarcoma. In this article, we review the current understanding of the histologic subtype classification of tumors previously diagnosed as MFH and its relation to clinical outcomes.

A comparison study of staging systems for bone sarcomas

A retrospective study of 250 patients treated at one institution was done to evaluate the prognostic significance of the new American Joint Committee on Cancer staging system compared with the Musculoskeletal Tumor Society staging system for patients with sarcomas of bone. Regarding the Musculoskeletal Tumor Society system, there were significant differences in survival among patients with Stage I, Stage II, and Stage III disease. There were no significant differences between patients with Stages I-A and I-B disease, nor between patients with Stages II-A and II-B disease. Similarly, regarding the new American Joint Committee on Cancer staging system, there were significant differences among patients with Stage I, Stage II, and Stage IV disease. No significant differences were seen between patients with Stages I-A and I-B disease, between patients with Stages II-A and II-B disease, nor between patients with Stages IV-A and IV-B disease. A significant advantage in the ability to predict prognosis for one staging system over the other staging system was not shown with the relatively small number of patients in this study.

Molecular classification of synovial sarcomas, leiomyosarcomas and malignant fibrous histiocytomas by gene expression profiling

In this study, we have used genome-wide expression profiling to categorise synovial sarcomas, leiomyosarcomas and malignant fibrous histiocytomas (MFHs). Following hierarchical clustering analysis of the expression data, the best match between tumour clusters and conventional diagnosis was observed for synovial sarcomas. Eight of nine synovial sarcomas examined formed a cluster that was characterised by higher expression of a set of 48 genes. In contrast, sarcomas conventionally classified as leiomyosarcomas and MFHs did not match the clusters defined by hierarchical clustering analysis. One major cluster contained a mixture of both leiomyosarcomas and MFHs and was defined by the lower expression of a set of 202 genes. A cluster containing a subgroup of MFHs was also detected. These results may have implications for the classification of soft tissue sarcomas, and are consistent with the view that sarcomas conventionally defined as MFHs do not represent a separate diagnostic category.

The use of clustering software for the classification of comparative genomic hybridization data. an analysis of 109 malignant fibrous histiocytomas

Malignant fibrous histiocytoma (MFH) is considered the most frequent soft-tissue sarcoma of late adult life. Nevertheless, the validity of this entity has been recurrently questioned by pathologists. Preliminary analyses by comparative genomic hybridization (CGH) of series of MFH have suggested that this tumor group is heterogeneous at the genomic level, and that at least two main genetic subgroups exist. We report an analysis by CGH of a large series of 109 MFH and on the use of clustering software for an objective classification of these tumors. We confirm our preliminary CGH results and demonstrate that two main clusters of tumors are present in the series analyzed.

[Does malignant fibrous histiocytoma exist?]

Malignant fibrous histiocytoma (MFH) has come to be regarded as the most common malignant neoplasm of the mesenchymal soft tissues. It designates a spectrum of tumors which share morphologic features that allow their inclusion in a distinct clinicopathologic setting, although being not uniform in their histogenesis and pathogenesis. Clinicopathologic variants include the following: the storiform-pleomorphic form of MFH, the myxoid type of MFH, the giant cell type of MFH and the inflammatory type. The latter group, the angiomatoid variant, has been reclassified within the fibrohistiocytic tumors of low malignant potential. Tissue culture, ultrastructural and immunohistochemical studies have both endorsed or refuted the validity of the concept. As a whole, these morphologic studies which attempted to characterize MFH were not able to delineate specific markers or to describe the phenotype of this sarcoma of supposed fibrohistiocytic lineage. There is growing evidence that MFH is a second component in another sarcoma and represents a morphologic modulation resulting from tumor progression. Recent cytogenetic and molecular genetic investigations are consistent with that hypothesis: a comparative analysis between the most frequent genomic imbalances observed in series of MFH and leiomyosarcomas (LMS) demonstrated that both tumors had similar recurrent imbalances. Immunohistochemical and molecular biologic investigations have shown similar targets of chromosome deletions in both tumors. A new classification of soft tissue sarcoma based on molecular parameters is nevertheless premature. The morphologic characterization of MFH and its sub-types provides the clinician with unique information in the management of these tumors, by identifying a spectrum of tumors with well-recognized clinical profiles.

Clinicopathologic re-evaluation of 100 malignant fibrous histiocytomas: prognostic relevance of subclassification

PURPOSE

Malignant fibrous histiocytoma (MFH) has been regarded as the most common soft tissue sarcoma (STS) in adults. Yet its true nature and the validity of this diagnostic concept have increasingly been questioned. Available data suggest that most patients with MFH can be subclassified into specific STS types, but the clinical relevance of such categorization has been argued. In a retrospective study, we reclassified 100 tumors of the extremity and trunk wall primarily diagnosed as MFH and analyzed the outcome.

PATIENTS AND METHODS

Patients were adults (median age, 70 years; range, 32 to 94 years). The median tumor size was 8 cm (range, 1 to 30 cm), and the thigh was the most common tumor location (n = 31). Median follow-up was 8 years (range, 3 to 16 years). The overall 5-year metastasis-free survival rate was 0.64. The tumors were reanalyzed histologically, immunohistochemically, and, where available, ultrastructurally, and were classified according to strict diagnostic criteria. Patients were staged according to the American Joint Committee on Cancer system, and prognoses were compared among different groups of the reclassified diagnoses, paying special attention to myogenic tumors.

RESULTS

In 84 of 100 tumors, a specific line of differentiation was either proved or strongly suggested. The most common diagnoses were myxofibrosarcoma (n = 22) and leiomyosarcoma (n = 20). Overall, 30 tumors could be grouped as some form of myogenic sarcoma. These tumors had a worse prognosis, even within the same American Joint Committee on Cancer stage, and a shorter time to metastasis than nonmyogenic tumors.

CONCLUSION

This retrospective study confirms that most so-called MFH can be subclassified by defined criteria; it provides evidence that such classification is clinically important. Specifically, pleomorphic STS showing myogenic differentiation are significantly more aggressive, a finding that allows planning future therapeutic trials.

Angiomatoid (malignant) fibrous histiocytoma: a peculiar low-grade tumor showing immunophenotypic heterogeneity and ultrastructural variations

To clarify the cellular differentiation features and facilitate diagnosis of angiomatoid (malignant) fibrous histiocytoma (AFH), four cases of AFH were examined by clinicopathologic, immunohistochemical and ultrastructural analyses. The age of the patients ranged from 10 to 24 years (mean, 17 years) and the sex distribution was equal. All cases were of subcutaneous origin: three arose in the trunk and one in the upper extremity. All patients presented with systemic symptoms, including inflammatory signs and anemia. After a mean follow up of 11 years 3 months, all patients were alive and well, although one patient twice developed local recurrence after surgery. All cases presented as multinodular, cystic and hemorrhagic tumors ranging in size from 4 to 11 cm (mean, 8 cm) and were characterized by sheets of bland spindle or round cells with oval nuclei within a circumscribed nodule often surrounded by a lymphocytic cuff. One tumor showed predominantly round cell morphology similar to Ewing's sarcoma/primitive neuroectodermal tumor. All cases (100%) exhibited immunoreactivity for vimentin, desmin, CD68 and CD57 (Leu-7). Three cases (75%) were positive for synaptophysin, and reactivity for alpha-smooth muscle actin, epithelial membrane antigen, neuron-specific enolase and CD99 (O-13) was present in two cases (50%) each. The three cases examined by electron microscopy had a mixture of fibrohistiocytic, myofibroblastic and undifferentiated cells containing cytoplasmic processes and dense-core granules. It is important for accurate diagnosis of this peculiar soft-tissue tumor to recognize that it has a variety of immunophenotypes, such as histiocytic, myofibroblastic, epithelial and neural, and may occasionally have a predominantly round cell morphology.

Indeterminate fibrohistiocytic lesions of the skin: is there a spectrum between dermatofibroma and dermatofibrosarcoma protuberans?

Routine histology and immunohistochemistry can usually distinguish dermatofibroma (DF) and dermatofibrosarcoma protuberans (DFSP). DF generally expresses factor XIIIa whereas DFSP generally expresses CD34. The authors report 10 cutaneous fibrohistiocytic lesions combining clinical, histologic, and immunohistochemical features of both DF and DFSP. The lesions had an average size of 1.2 cm (range, 0.4-2.7 cm), and occurred on the trunk (n = 6), extremities (n = 3), and face (n = 1) of four men and six women (average age, 30.6 yrs; age range, 15-50 yrs). Eight lesions exhibited acanthosis and densely cellular fascicles with focal storiform areas. All had keloidal collagen, infiltrated the subcutis in a honeycomb pattern, and had low mitotic counts (0 to 4 mitoses per square millimeter). All were diffusely immunoreactive for factor XIIIa (30%-60% of the neoplastic cells) as well as CD34 (20%-70%). This series raises the possibility of a biologic spectrum between DF and DFSP; however, double-immunolabeling studies showed no notable coexpression of factor XIIIa and CD34 by individual cells, suggesting coexistence of two different cellular populations. After an average follow up of 22.3 months (range, 10-46 mos) in six cases, a single recurrence was documented. The ambiguous histologic features and the potential for local recurrence suggest that performing a complete excision may be prudent in these diagnostically indeterminate lesions.

Combined dermatofibroma: co-existence of two or more variant patterns in a single lesion

AIMS

Based on a series of 25 cases, we define and characterize combined dermatofibroma, a tumour comprising two or more variant patterns of dermatofibroma in a single lesion.

METHOD AND RESULTS

Dermatofibroma may present with a wide variety of architectural, cellular or stromal peculiarities. Architectural peculiarities include deep penetration, atrophy, collarette formation, fascicular to plexiform architecture, massive haemorrhage, prominent haemangiopericytoma-like vascularity and palisading; cellular peculiarities the presence of epithelioid cells, clear cells, granular cells, prominent myofibroblastic differentiation and atypical giant cells ('monster cells'); or stromal peculiarities such as prominent sclerosis, mucin, haemosiderin and cholesterotic deposits. In combined dermatofibromas two or more of these features are seen in complex or inhomogenous combination such as the silhouette of a deep penetrating dermatofibroma with an 'ordinary' storiform pattern in the upper and granular cell differentiation in the lower part of the lesion; or a dermatofibroma with ordinary features in the upper, prominent sclerosis in the middle and clear cells in the lower portion of the lesion; or the characteristic epidermal collarette and cells of epithelial cell histiocytoma with a plexiform ('neurothekeoma-like') architecture surrounded by a myxoid stroma with spindle-shaped to stellate cells. Clinically, these lesions preferentially occur on the lower extremities of young to middle-aged females, frequently with the diagnosis of a fibrohistiocytic lesion. Apart from one recurrence follow-up was uneventful in all other cases. Immunohistochemically, lesions are consistently positive with KiM1p, variably positive for factor XIIIa, smooth muscle specific actin and with KP1 (CD68), NK1C3 and E9.

CONCLUSION

Recognition of combined dermatofibroma allows the histopathologist to apply a confident benign label to unusual lesions which might otherwise elude diagnosis, or tempt description of 'new' entities and to avoid a misdiagnosis of malignancy.

Lichenoid, erosive and ulcerated dermatofibromas. Three additional clinico-pathologic variants

On the occasion of a case of dermatofibroma with histological lichenoid features, we reviewed from our files all the cases in which the epidermis, usually hyperplastic in dermatofibroma, was, in some way, partially or completely destroyed. Among a total of 484 dermatofibromas, we found three lichenoid, six erosive and two ulcerated cases. In the three lichenoid cases, the columnar epidermal basal cells were lacking (squamotization of the basal layer) and in two of them there was a cleft between the epidermis and the dermatofibroma. Three of the six eroded cases were large pedunculated dermatofibromas with inflammatory phenomena of variable intensity. One case was in the center of a plaque of lichen simplex chronicus with some eroded area. In the other two cases, as well as in the two ulcerated lesions, neither inflammation nor epidermal changes usually attributed to rubbing or scratching were seen. Only in three of the eleven cases dermatofibroma was proposed (with question mark) as a clinical diagnosis. Both follow-up and histopathology supported the benign nature of these cases. We may conclude that: i) Lichenoid, erosive and ulcerated changes in dermatofibroma are infrequent phenomena which may make a clinical diagnosis difficult; and ii) in the presence of an otherwise histopathologically typical dermatofibroma, erosion and ulceration should not be considered as suspicious of malignancy.

Primary fibrosarcoma and malignant fibrous histiocytoma of bone--a comparative ultrastructural study: evidence of a spectrum of fibroblastic differentiation

As primary bone fibrosarcoma (FS) and malignant fibrous histiocytoma (MFH) have similar clinical, radiographic, or survival manifestations, ultrastructural and immunohistochemical studies were undertaken to determine the differentiation pathways of constituent malignant cells. Twelve cases of primary intraosseous FS and MFH were selected for this ultrastructural comparative study and were analyzed for fibroblastic or modified fibroblastic differentiation. There were 4 FS cases and 8 MFH cases, of which 5 were storiform-pleomorphic, 2 were giant cell, and 1 was myxoid type. All FS consisted of spindle fibroblasts with a prominent rough endoplasmic reticulum and Golgi apparatus, variable amounts of vimentin intermediate filaments, and extracellular collagen fibrils. The MFH were composed of a mixture of spindle and pleomorphic fibroblasts (8/8), histiofibroblasts (4/8), and myofibroblasts (3/8). Variable numbers of undifferentiated cells were found in both tumors. In conclusion, fibroblastic differentiation and collagen production was noted in all cases. The often pleomorphic histiofibroblasts present in some MFH cases most likely represent "modified fibroblasts," similar to myofibroblasts. These findings support the hypothesis that the fibroblast and its variants are the predominant cell types found in these tumors, suggesting that the diagnostic entity MFH should be classified as a pleomorphic fibrosarcoma.

Malignant fibrous histiocytoma (MFH). A comparison of MFH in man and animals. A critical review

This review gives information about localization and types of MFH in man and animals such as mouse, rat, cat, dog, opossum, cattle, horse and birds [e.g. mallard (a wild duck)]. Furthermore, this paper reports about cell culture dealing with MFH. The aim of this publication is to show that MFH originates from a primitive mesenchymal stem cell, fibroblastoid cell and fibroblasts. Histiocytes are, according to the literature in a small amount constituents of MFH and are reactive cells or without any meaning. In our own studies using rats [strain: Chbb: THOM (SPF)] the characteristic storiform or cartwheel pattern of tumour cells were evident. The cells were elongated, rich in endoplasmic reticulum and possessed no or very few lysosomes. The cells were predominantly fibroblasts and fibroblastoid cells. These cells were intermingled with giant cells. In other species mentioned above, the MFH showed very similar histological features. Our own results and findings obtained from the literature support our concept that the MFH represents a primitive phenotype or pleomorphic sarcoma which may differentiate in one or more directions. Histiocytes are not a neoplastic component.

[Cellular "neurothekeoma": an epithelioid variant of dermatofibroma?]

AIMS

The present series describes 15 cellular neurothekeomas whose clinicopathologic features indicate a close relationship to dermatofibroma.

METHODS

Retrospective clinicopathologic study.

RESULTS

Lesions preferentially occurred in adolescents to young adults on the upper half of the body, often clinically diagnosed as some kind of fibrohistiocytic tissue response. Besides characteristic whorled nests to fascicles of palely eosinophilic epithelioid cells all lesions showed variable clues pointing to dermatofibroma: acanthosis, ill-defined storiform periphery, peripherally accentuated prominent sclerosis and lymphocytic demarcation/infiltration. All cases were positive with NK1C3 (CD 57), Ki-M1p and proliferating cell nuclear antigen, 7 for neuron specific enolase, 5 for factor XIIIa, 6 for smooth muscle actin and 3 with E9, an anti-metallothionein marker. These findings are similar to other types of dermatofibromas, the variability of the profile being best explained by time cycle and function dependent changes. Ultrastructurally, two cases showed microfilaments, attachment plaques, prominent pinocytosis and focal remnants of basal lamina. A careful study of data and microphotographs from the literature reveals that in many cases similar conclusions can be reached. Obvious discrepancies are most likely due to the confusion with myxoid neurothekeoma, a well circumscribed, more spindly and myxoid, S 100 positive lesion of Schwannian origin.

CONCLUSION

According to our results cellular neurothekeoma seems to be a whorled-nested to plexiform epithelioid variant of dermatofibroma.

[Fibrohistiocytic skin lesions]

AIMS

A new unifying concept of fibrohistiocytic skin lesions.

METHODS

Retrospective clinicopathologic study of more than 2,000 dermatofibromas (DF) recruited over the last two decades.

RESULTS

As the least common denominator all DF show a reactive fibrohistiocytic tissue response with variable epidermal hyperplasia, peripheral sclerosis and peripherally accentuated lymphohistiocytic tissue response. The histological, immunohistochemical and ultrastructural profile varies according to the time cycle as well as the fibro-myofibrohistiocytic differentiation of the lesions. From a conceptual point of view such lesions are best grouped into three categories: 1. DF with cellular/stromal pecularities. All classic variants, from the first description by Unna in 1894 to lesions described in 1978, namely DF, (benign) fibrous histiocytoma, histiocytoma cutis, sclerosing hemangioma, nodular subepidermal fibrosis or fibrous xanthoma, fall into this category; moreover, many of the clinicopathologic variants described over the last two decades such as granular cell, clear cell, myofibroblastic, sclerosing, monster cells, atypical ("pseudosarcomatous"), haemosiderotic ("elusive"), cholesterotic, and myxoid variants. 2. DF with architectural pecularities such as deep penetrating, atrophic, aneurysmal ("angiomatoid"), haemangiopericytoma-like, palisading and ossifying variants. And 3. DF with both cellular/stromal and architectural pecularities including those with a homogenous mixture of components as seen in epithelioid, cellular benign variants, smooth muscle proliferation in DF, multinucleate cell angiohistiocytoma, cellular neurothekeoma, and dermal plexiform fibrohistiocytic tumour; as well as those with heterogeneous mixture of components in composite or mixed dermatofibromas.

CONCLUSION

DF is common, the clinicopathological variability manyfold, and their misinterpretation as malignancy such as dermatofibrosarcoma protuberans or Kaposi sarcoma not rare. Such cases have important clinical implications such as unnecessary investigations, controls and livelong anxiety of patients.

[Dermatofibroma. A clinico-pathologic classification scheme]

Dermatofibroma is a common benign fibrohistiocytic lesion which presents with a wide variety of clinicopathologic variants. This may cause great difficulties in delineation from a variety of benign and malignant tumours. According to their peculiarities we differentiate: 1. Dermatofibromas with architectural peculiarities like deep penetrating, atrophic, giant, aneurysmal ("angiomatoid"), haemangiopericytoma-like, palisading or ossifying variants. 2. Dermatofibromas with cellular/stromal peculiarities like clear cell, granular cell, myofibroblastic, sclerotic, monster cell, atypical ("pseudosarcomatous"), elusive ("haemosiderotic"), cholesterotic, and myxoid variants. 3. Dermatofibromas with architectural and cellular/stromal peculiarities in homogenous arrangement like epithelioid cell, cellular benign variants, with smooth muscle proliferation, basal cell carcinoma-like, pseudolymphomatous, multinucleate cell angiohistiocytoma, cellular neurothekeoma, plexiform fibrohistiocytic tumour, plexiform xanthoma and plexiform xanthomatous tumour. 4. Complex or composite dermatofibromas with two or more architectural and cellular/stromal peculiarities in inhomogenous arrangement, e.g. silhouette of an epithelioid cell histiocytoma with plexiform fascicles of cellular neurothekeoma and granular cell features.

Malignant fibrous histiocytoma of bone: conventional X-ray and MR imaging features

OBJECTIVE

To evaluate the conventional X-ray and MR imaging features of malignant fibrous histiocytoma (MFH) of bone.

DESIGN

MRI examinations and conventional radiographs were reviewed in 39 patients with biopsy-proven MFH. Imaging characteristics were analyzed and the differential diagnoses assessed in a masked fashion by two experienced radiologists.

RESULTS

Typical X-ray features included aggressive, destructive tumor growth centrally located in the metaphysis of long bones. Periosteal reactions and expansive growth were rarely seen. On MR images extraosseous tumor spread was frequently noted. On T2-weighted images and contrast-enhanced T1-weighted images most of the tumors displayed an inhomogeneous, nodular signal pattern with peripheral Gd-DTPA enhancement.

CONCLUSIONS

Although several MR imaging criteria were typical for MFH none of them was specific. X-ray diagnosis of MFH may also prove difficult, with the main differential diagnosis being metastasis in the older and osteosarcoma in the younger population.

Cellular 'neurothekeoma': an epithelioid variant of dermatofibroma?

AIMS

Cellular neurothekeoma is a rare benign cutaneous neoplasm with conflicting opinions regarding its histogenetic origin (nerve sheath, smooth muscle, myofibroblasts) as well as its relation to myxoid neurothekeoma (nerve sheath myxoma). The present series describes 15 cases whose clinicopathological features indicate a relationship to dermatofibroma.

METHODS AND RESULTS

In this retrospective clinicopathological study, the lesions preferentially occurred in adolescents to young adults on the upper half of the body, often clinically diagnosed as some kind of fibrohistiocytic tissue response. Besides characteristic whorled nests to fascicles of palely eosinophilic epithelioid cells, all lesions showed variable clues pointing to dermatofibroma: acanthosis, ill-defined storiform periphery, peripherally accentuated prominent sclerosis and lymphocytic demarcation/infiltration. Immunohistochemically, all cases were positive with NK1C3 (CD57), KiM1p and proliferating cell nuclear antigen, seven were positive for neurone specific enolase, five for factor XIIIa, six for smooth muscle specific actin and three for E9, an antimetallothionein marker. These findings are similar to those of conventional dermatofibromas, the variability of the profile being best explained by time cycle and function dependent changes. Ultrastructurally, two cases showed microfilaments, attachment plaques, prominent pinocytosis and focal remnants of basal lamina. A careful study of the data and photomicrographs from the literature reveals that in many cases similar conclusions could be reached. Obvious discrepancies are most likely due to the confusion with myxoid neurothekeoma, a well circumscribed, more spindly and myxoid, S100 positive lesion of Schwannian origin.

CONCLUSION

The appearance of dermatofibromas is markedly influenced by architectural, e.g. in deep penetrating dermatofibroma, and/or cellular/stromal criteria, e.g. in epithelioid cell histiocytoma or sclerosing dermatofibroma. Cellular neurothekeoma seems to be a variant of dermatofibromas with both architectural and cellular/stromal peculiarities, i.e. plexiform pattern, epithelioid cytology and stromal sclerosis.

Detection of numerical chromosomal changes in 20 malignant fibrous histiocytomas by FISH

We investigated 20 malignant fibrous histiocytomas (MFHs) with the help of specific centromeric probes for chromosomes 1, 3, 4, 6, 8, 9, 12, 16, 17 and 18. The results show a broad variation in the number of signals per nucleus. However, tumors can be assigned into four groups: i) with mostly disomic clones, ii) with a high percentage of polysomic clones, iii) with a considerable amount of monosomic and nullisomic clones and iv) with a tendency in both directions. A gain of spots per nucleus takes place in 75-100% of the investigated tumors - the highest incidence occurring with respect to chromosome 3. A loss of spots per nucleus occurred in 20-60% of the tumors - predominantly with respect to chromosome 1.

Malignant fibrous histiocytoma: histomorphological pattern or tumor type

During the past years MFH has obviously been used as a diagnostic waste basket for hard to classify tumours of all kinds. Immunohistochemistry revealed insights into cellular differentiation of neoplastic proliferations, also raising new questions because of unexpected antigen expression, as, for instance, cytokeratins in MFH. Thus, a number of tumours originally diagnosed as MFH could be reclassified, i.e., as leiomyosarcoma, melanoma or anaplastic carcinoma. Nevertheless, there remain a certain number of sarcomas which lack any evidence of special cellular differentiation. These proliferations of primitive mesenchymal or fibroblastic cells, often with a typical histological, storiform pattern, qualify as MFH. Using these strict criteria, the diagnosis of MFH will become rarer, though not obsolete (like hemaugioperizytoma years ago!).

Inflammatory leiomyosarcoma: a morphological subgroup within the heterogeneous family of so-called inflammatory malignant fibrous histiocytoma

Twelve cases of inflammatory leiomyosarcoma are presented. These tumours arose in the deep soft tissues of the trunk and proximal limbs. The age of the patients ranged from 13-53 years (median 36 years); there was an approximately equal sex ratio. Follow-up data was available for nine patients (mean duration 3.3 years); local recurrence occurred in three and lung metastases in one. Lesions were spindle cell neoplasms with fascicular areas which occupied between 5% and 80% of the tumour. Areas with a distinct storiform pattern were also seen in 10 cases. A prominent inflammatory cell component was evident in all tumours, often masking the neoplastic spindle cells. Histiocytes were identified in all cases, with aggregates of xanthoma cells seen in eight tumours. In 10 cases there was also a dense lymphoid infiltrate and in two a marked polymorphonuclear leukocyte infiltrate was evident. Immunohistochemistry showed in all tumours that the spindle cells stained positively for myogenic markers (8 of 12 positive for desmin, 10 of 12 for alpha smooth muscle actin and 11 of 12 for HHF-35). CD68 was expressed by the histiocytic infiltrates. Many of these tumours were diagnosed initially as inflammatory malignant fibrous histiocytoma. We provide evidence that at least one subset of neoplasms, which would have been formerly classified under this rubric, in fact show smooth muscle differentiation. Further studies are required to investigate the possibility that other tumour types or lines of differentiation may be present within the category of so-called inflammatory malignant fibrous histiocytoma.

Classification and grading of soft-tissue sarcomas

This article provides an overview of the classification of soft-tissue sarcomas as influenced by modern histopathologic techniques. The overview is followed by a practical grading system for these tumors based on a study of 282 eligible patients. The primary tumors of this trial were adequately treated. The quantitative data (mitotic count and size of the tumor) were based on the results of the statistical analysis.

Staging of malignant tumours of the foot

Tumours of the foot in general, and malignant tumours in particular, are extremely rare. In the absence of a large series it is necessary to resort to surgery based on "principles" and not on experience or on data drawn from retrospective clinical studies. Enneking's "Surgical Staging System" (S.S.S) is a method of staging musculo-skeletal tumours which has been universally adopted-for several years and which is based, as already known, on the concept of anatomo-surgical "compartments". In the particular case of the foot, the S.S.S. suggests the surgical criteria specific to each anatomical region. The authors illustrate the principles with some examples taken from their experience, evaluating the surgical, oncological and functional aspects.

Angiomatoid "malignant fibrous histiocytoma": an immunohistochemical study indicative of myoid differentiation

Six cases of angiomatoid malignant fibrous histiocytoma (MFH), the rarest subtype of MFH, have been studied immunohistochemically using a broad panel of commercially available antisera in formalin-fixed, paraffin-embedded tissue in an attempt to define the pattern of differentiation shown by this unusual tumor. As has been reported in the more common types of MFH, no evidence of histiocytic differentiation was found. However, five cases strongly expressed desmin (DER-11) and two also expressed muscle actin (HHF 35). All tissues examined were negative for myoglobin and alpha-smooth muscle actin. These results provide good evidence for some sort of myogenic or possibly myofibroblastic differentiation in angiomatoid MFH. Given its clinicopathologically and immunohistochemically distinctive features, which are very different from the other variants of MFH, redesignation of angiomatoid MFH as a low-grade myogenic sarcoma of uncertain histogenesis is tentatively proposed. The new term angiomatoid myosarcoma is suggested.

Primary intracranial sarcomas: histopathological features of 19 cases

Nineteen primary intracranial sarcomas out of a total of about 25,000 brain tumour biopsies are reported. Subtypes included malignant fibrous histiocytoma (6 cases), leiomyosarcoma (3), rhabdomyosarcoma (2), angiosarcoma (2), and one case each of fibrosarcoma, low-grade fibromyxoid sarcoma, malignant ectomesenchymoma, mesenchymal chondrosarcoma, differentiated chondrosarcoma and Ewing's sarcoma. Histological and immunohistochemical features corresponded to those of extracranial sarcomas. Nests of pleomorphic astrocytes mimicking glioma were detected in the five storiform-pleomorphic malignant fibrous histiocytomas. Our results indicate that intracranial sarcomas can be classified like their extracranial counterparts. The low incidence compared with earlier series is related to changes in classification and progress in histogenetic clarification.

A rational classification of angiofibromas of the post nasal space

Angiofibromas of the post nasal space have the potential to extend in all directions along predetermined pathways with a definite mode and chronological pattern. In order to understand their clinical behaviour, methods of treatment and prognosis, a system of clinical staging based on conventional and tomographic observations has been found useful in this series of cases. The classification has been evolved according to the extent of the tumour involvement but also the age of onset, duration, size and area of encroachment including the surgical approach and consequent prognosis. Deficiencies in the earlier classifications are discussed.

Malignant fibrous histiocytoma with epithelial differentiation?

A case of recurrent soft part sarcoma with focal areas showing epithelial differentiation in the right thigh in a 78-year-old woman is reported. The primary tumor consisted of myxoid areas and solid areas, in which relatively uniform epithelioid tumor cells were arranged in sheets, whereas pleomorphism and a storiform pattern appeared in the recurrent tumors. Thus this tumor was suspected to be a malignant fibrous histiocytoma. However, further studies showed unexpected ultrastructural and immunohistochemical features. Cytokeratin immunoreactivity and tonofilamentlike structures probably indicated epithelial differentiation of some tumor cells. From the clinical and histological findings, this tumor should be identified as a malignant fibrous histiocytoma with phenotypic expressions of epithelial cell.

Primary tumours of the thymus in the rat

The features of 192 primary thymic tumours occurring in the rat are described. Of these neoplasms, 170 were classified as benign thymomas, one as a benign fibrous histiocytoma, 20 as various types of malignant thymoma, 3 lympho-epithelioma-like carcinomas, one mixed small cell undifferentiated-squamous cell carcinoma, one sarcoma-like carcinoma, 4 undifferentiated carcinomas, 11 squamous cell carcinomas and the one remaining tumour as a carcinoid. A mouse, anti-epithelial, monoclonal antibody, lu-5, was used to confirm the epithelial nature of the malignant thymomas, and neuron-specific enolase to confirm the diagnosis of carcinoid. The tumours showed many features in common with those reported in man.

Renal hamartoma associated with renal cell (Grawitz) tumor: another indication that Grawitz tumors are carcinosarcomas

We report a case of renal hamartoma (angiofibroma) which contained nests of renal cell (Grawitz) tumor and review the literature regarding this subject. We believe that the finding of Grawitz tumor cells within a mesodermal tumor supports our hypothesis that renal cell (Grawitz) tumors are of mixed (mesodermal and endodermal) origin, that is, they show at least one important biological characteristic of carcinosarcomas.

The pathology of malignant fibrous histiocytoma of bone. A study of 130 patients

Since 1927, 130 patients with well-documented malignant fibrous histiocytoma of bone have been diagnosed and treated at Memorial Hospital for Cancer and Allied Diseases. This sarcoma is 10 times less frequent than osteogenic sarcoma in this hospital. It most commonly occurred spontaneously (72%), whereas in the rest (28%) it followed previous radiation or various pre-existent osseous conditions, most often Paget's disease. The appendicular skeleton was the commonest site of involvement. The majority of the patients were middle-aged or older adults with a mean of 40.5 years of age; only 21.5% were 21 years or younger. Histologically, the lesions were subclassified as fibrous (62%), histiocytic or xanthomatous (30%), and malignant giant cell tumor (8%) variants. Older patients were more likely to have a secondary malignant fibrous histiocytoma, especially following radiation or Paget's disease. Overall survival estimates at 2 years and 5 years were 71% and 53%, respectively. Survival was not dependent on the histologic subtype of the lesion, but was strongly influenced by the histologic grade of malignancy. Important prognostic factors were the age of the patients and whether the lesions were primary de novo or secondary sarcomas: the older patients and those with secondary lesions did substantially worse.