Peripheral nerve sheath differentiation in malignant soft tissue tumours: an ultrastructural and immunohistochemical study

Undifferentiated and dedifferentiated soft tissue neoplasms: Immunohistochemical surrogates for differential diagnosis

Undifferentiated soft tissue sarcomas (USTS) are described in the current World Health Organization Classification of Soft Tissue and Bone Tumours as those showing no identifiable line of differentiation when analyzed by presently available technologies. This is a markedly heterogeneous group, and the diagnosis of USTS remains one of exclusion. USTS can be divided into four morphologic subgroups: pleomorphic, spindle cell, round cell and epithelioid undifferentiated sarcomas, with this combined group accounting for up to 20% of all soft tissue sarcomas. As molecular advances enable the stratification of emerging genetic subsets within USTS, particularly within undifferentiated round cell sarcomas, other groups, particularly the category of undifferentiated pleomorphic sarcomas (UPS), still remain difficult to substratify and represent heterogeneous collections of neoplasms often representing the common morphologic endpoints of a variety of malignant tumors of various (mesenchymal and non-mesenchymal) lineages. However, recent molecular developments have also enabled the identification and correct classification of many tumors from various lines of differentiation that would previously have been bracketed under 'UPS'. This includes pleomorphic neoplasms and dedifferentiated neoplasms (the latter typically manifesting with an undifferentiated pleomorphic morphology) of mesenchymal (e.g. solitary fibrous tumor and gastrointestinal stromal tumor) and non-mesenchymal (e.g. melanoma and carcinoma) origin. The precise categorization of 'pleomorphic' or 'undifferentiated' neoplasms is critical for prognostication, as, for example, dedifferentiated liposarcoma typically behaves less aggressively than other pleomorphic sarcomas, and for management, including the potential for targeted therapies based on underlying recurrent molecular features. In this review we focus on undifferentiated and dedifferentiated pleomorphic and spindle cell neoplasms, summarizing their key genetic, morphologic and immunophenotypic features in the routine diagnostic setting, and the use of immunohistochemistry in their principal differential diagnosis, and highlight new developments and entities in the group of undifferentiated and dedifferentiated soft tissue sarcomas.

Clear Cell Sarcoma of Tendons and Aponeuroses

Fifty-eight previously unreported cases of clear cell sarcoma of tendons and apo neuroses occurring in 29 males and 29 females with a median age of 31 years are presented. The distal extremities were most frequently involved (58%), followed by the limbs and limb girdles (33%), and trunk (9%). Median tumor size was 2.5 cm (range, 0.6-9 cm). Kaplan-Meier estimates revealed a 5-year survival rate of 63%. Eleven of 43 patients (26%) had local recurrences at a median interval of 33 months. Metastases occurred in 20 of 45 cases (44%) at a median interval of 26 months; 19 of 20 patients with metastases died of the disease. The most common metastatic site was the lungs (11 cases), followed by bone (9 cases), and lymph nodes (8 cases). Clear cell sarcoma had a stereotypic morphology consisting of packeted arrangements of uniform, round to fusiform cells with eosinophilic to clear glycogen-rich cytoplasm, and prominent nucleoli, as well as multinucleated tumor cells with a wreath-like arrangement of nuclei. S100 protein was detected in all 44 cases studied, vimentin in 36, and HMB45 stained 36. Twenty-six cases were studied with antibodies directed against proliferating cell nuclear antigen. Neither the intensity of proliferating cell nuclear antigen staining, percentage of positive cells, nor the combined score of these two variables corresponded with mitotic rate or survival. Increasing size (as a continu ous variable) and necrosis were found to be independent adverse prognostic factors by multivariate analysis. Int J Surg Pathol 1 (2):89-100, 1993

Synovial sarcoma: defining features and diagnostic evolution

Synovial sarcoma (SS) is a malignant mesenchymal neoplasm with variable epithelial differentiation, with a propensity to occur in young adults and which can arise at almost any site. It is generally viewed and treated as a high-grade sarcoma. As one of the first sarcomas to be defined by the presence of a specific chromosomal translocation leading to the production of the SS18-SSX fusion oncogene, it is perhaps the archetypal "translocation-associated sarcoma," and its translocation remains unique to this tumor type. Synovial sarcoma has a variety of morphologic patterns, but its chief forms are the classic biphasic pattern, of glandular or solid epithelial structures with monomorphic spindle cells and the monophasic pattern, of fascicles of spindle cells with only immunohistochemical or ultrastructural evidence of epithelial differentiation. However, there is significant morphologic heterogeneity and overlap with a variety of other neoplasms, which can cause diagnostic challenge, particularly as the immunoprofile is varied, SS18-SSX is not detected in 100% of SSs, and they may occur at unusual sites. Correct diagnosis is clinically important, due to the relative chemosensitivity of SS in relation to other sarcomas, for prognostication and because of the potential for treatment with specific targeted therapies in the near future. We review SS, with emphasis on the diagnostic spectrum, recent immunohistochemical and genetic findings, and the differential diagnosis.

Spindle Cell Sarcomas

Information is presented on the pathology of spindle cell sarcomas. Synovial sarcoma, malignant peripheral nerve sheath tumor, fibrosarcoma, inflammatory myofibroblastic tumor, low-grade myofibrosarcoma, leiomyosarcoma, spindle cell rhabdomyosarcoma, and endothelial neoplasms are discussed in terms of an overview of the tumor, microscopic and gross features, diagnostic techniques, genetic markers, differential diagnosis, clinical details, and prognosis.

Immunohistochemistry in diagnosis of soft tissue tumours

Immunohistochemistry in soft tissue tumours, and especially sarcomas, is used to identify differentiation in the neoplastic cells. In some cases, specific antigens are expressed; however, an initial panel of antibodies is often required in order to establish the broad lineage, with a subsequent, more focused, panel to allow classification. Immunohistochemical evaluation must be employed with the clinical picture, the morphology, and, when necessary, other ancillary techniques such as molecular genetics and cytogenetics. Whereas some diagnoses are evident on morphology, many soft tissue neoplasms are seen microscopically as spindle cell, epithelioid cell, small round cell or pleomorphic tumours that need to be further characterized. This article reviews selected applications of immunohistochemistry in the diagnosis of each of the principal morphological groups, concentrating on areas of most use in daily practice.

Low-grade malignant soft-tissue perineurioma: interphase fluorescence in situ hybridization

Perineuriomas are usually benign soft-tissue tumors that arise from perineurial cells of the peripheral nerve sheath. Low-grade malignant perineurioma is a rare type of perineurioma, presenting with infiltrative growth, low mitotic activity, and a lack of necrosis. This report describes a case of low-grade malignant perineurioma in a 60-year-old man who presented with a growing tumor on the dorsal side of his left wrist. The tumor was surgically excised and showed no adhesion to the surrounding muscle and no continuity with nerves. There was no evidence of recurrence or metastases 12 months after surgery. Histology indicated that the tumor contained hypercellular and hypocellular areas with spindle-shaped cells proliferating in storiform patterns or perivascular whorling. There was moderate infiltrative growth into the surrounding tissue. There was an evident central infarction but no coagulative necrosis. Mitotic figures were observed at 5/10 high-power fields. On immunohistochemistry tumor cells were found to be positive for epithelial membrane antigen, glucose transporter protein 1, and claudin-1. Approximately 18.4% of tumor nuclei were labelled for Ki-67. Interphase fluorescence in situ hybridization on paraffin sections indicated a loss of chromosome 13. This suggests that chromosome 13 abnormalities could also be involved in perineurioma with low-grade malignant potential.

A case of fibroblastic low-grade malignant peripheral nerve sheath tumor--a true neurofibrosarcoma

The authors report a case of low-grade retroperitoneal malignant peripheral nerve sheath tumor (MPNST) showing Schwannian and fibroblastic differentiation in individual tumor cells. The tumor was detected in a 29-year-old male and posed diagnostic difficulty because of the unusual morphologic and immunophenotypic features. Morphologic examination of the H&E sections revealed a rather circumscribed, highly vascular, moderately cellular spindle cell tumor. The neoplastic cells were arranged in vague, short fascicles, distributed haphazardly amid hemangiopericytoma-like vascular channels, and showed occasional whorls. Myxoid stroma and keloid-like collagen bundles were frequently seen. There were satellite nodules outside the main tumor mass and low mitotic activity but no necrosis. The tumor cells stained strongly and diffusely for both S-100 protein and CD34. Electron microscopy revealed cells with processes and focal lamina, and prominent rough endoplasmic reticulum. Although the capacity of MPNST to exhibit divergent differentiation is well known, fibroblastic differentiation is generally poorly and inconsistently documented. The present case represents an unambiguous demonstration of the co-expression within individual tumor cells of Schwannian and fibroblastic differentiation in a low-grade MPNST. The literature on this subject is reviewed.

The comparative roles of electron microscopy and immunohistochemistry in the diagnosis of soft tissue tumours

Electron microscopy has contributed to the diagnosis of soft tissue tumours for four decades, and immunohistochemistry for two. Because of its relative ease of use and interpretation, the latter technique has become extensively and routinely applied to identify lines of differentiation in benign soft tissue tumours and in sarcomas. The use of electron microscopy has declined but retains a role because few antibodies are wholly specific or fully sensitive, some tumours are polyphenotypic or divergent in differentiation, and others have no specific antigens. Immunohistochemistry is superior in diagnosis of smooth muscle tumours, small round cell tumours, sarcomas with epithelioid morphology, and most synovial sarcomas. Electron microscopy is of particular value for peripheral nerve sheath tumours, marker-negative synovial sarcomas, pleomorphic sarcomas and mesotheliomas. As with all adjunctive techniques, immunohistochemistry and electron microscopy should be used in a complementary fashion according to the nature of the diagnostic problem.

Low-grade malignant perineurioma (perineurial sarcoma) of soft tissue: a potential diagnostic pitfall on fine needle aspiration

A case of low-grade malignant perineurioma presenting as a mass in the thigh is described. The patient was a 76-year-old woman with an enlarging painful mass on her right lateral thigh over the past 2 months. Thorough clinical and radiological studies did not reveal any evidence of tumor elsewhere. The patient underwent fine needle aspiration of the mass, which revealed pleomorphic spindle cells in small clusters or dispersed as single cells within myxoid stroma, cytologically consistent with a high-grade sarcoma. At surgery, the tumor was found to be entirely confined within the muscle. Grossly, the tumor measured 6.5 cm in greatest diameter and showed a gray-white fleshy cut surface that was well circumscribed but unencapsulated. Histologic examination showed a highly cellular spindle cell proliferation embedded within myxoid stroma. The tumor cells showed mild to moderate nuclear pleomorphism with minimal mitotic activity. No evidence of hemorrhage or necrosis was noted. The tumor irregularly invaded the surrounding skeletal muscle. Immunohistochemical studies showed weak membranous positivity for epithelial membrane antigen and focal cytoplasmic positivity for CD34; stains for smooth muscle actin, cytokeratin AE1/AE3, desmin, CD56, H-caldesmon, calponin, and S-100 protein were negative. Electron microscopy showed cells with thin, elongated cytoplasmic processes extending along connective tissue in a parallel, onion-like arrangement and prominent subplasmalemmal pinocytotic activity. The marked pleomorphism displayed on fine needle aspiration observed in this case can lead to a mistaken diagnosis of high-grade sarcoma resulting in unnecessarily aggressive management.

Perineurioma: a clinicopathological study of eight cases

AIMS

Perineuriomas (PN) are uncommon, benign neoplasms that mimic a number of benign and malignant soft tissue lesions. There are two main forms: a rare intraneural PN (IPN), and a relatively more common extraneural soft tissue PN (STPN) including a conventional form (STPNc), sclerosing (SPN), reticular and lipomatous variants. Their diagnosis requires immunohistochemical (IHC) and/or ultrastructural (US) confirmation of perineurial cell differentiation. This study aims to review the clinicopathological features of eight PN we encountered recently, to raise awareness of PN as an entity and to highlight the differential diagnoses which include potentially aggressive lesions.

METHODS

Clinical, histological, IHC and US features of seven STPN and one IPN were studied.

RESULTS

The eight PN arose in the limbs of six females and two males aged 30-58 years. Five STPN occurred in subcutis, one intramuscularly and one intradermally. The STPN were well-circumscribed, multinodular growths. STPNc contained bland spindle cells with long cytoplasmic processes arranged in lamellae, storiform patterns and whorls. Three SPN were acrally located and additionally contained small epithelioid cells in cords and clusters in a myxohyaline stroma with extensive sclerosis. One SPN had giant collagen rosettes of spiral collagen. The IPN showed 'pseudo-onion bulbs' of perineurial cells. All PN were at least focally EMA positive, six of eight were Claudin-1 positive and all were S100 protein negative. Common US features were organelle-poor cell processes, many pinocytotic vesicles, sparse intermediate filaments, and tight junctions and patchy external lamina. There were no recurrences (follow-up 1-49 months).

CONCLUSION

PN has a variable morphology and can mimic many benign, borderline and malignant lesions, the differential diagnoses of which are discussed. When confronted with a subcutaneous (in particular) spindle and/or epithelioid cell lesion, EMA/Claudin-1 stains and/or US are essential to identify PN and thereby avoid inappropriately aggressive therapy.

Immunohistochemical demonstration of EMA/Glut1-positive perineurial cells and CD34-positive fibroblastic cells in peripheral nerve sheath tumors

To clarify the cellular composition of various peripheral nerve tumorous lesions (traumatic neuroma, 5 cases; schwannoma, 10 cases; neurofibroma, 14 cases; perineurioma, 3 cases; conventional malignant peripheral nerve sheath tumor (MPNST), 7 cases; perineurial MPNST, 4 cases), expression of several markers specific to nerve sheath cells, including glucose transporter protein 1 (Glut1) and CD34, were immunohistochemically investigated with highly sensitive detection methods. In normal nerves and neuromas, perineuriums were positive for Glut1 as well as for epithelial membrane antigen (EMA), and there were some CD34-positive fibroblast-like cells in the endoneurium. Schwannomas consisted principally of S-100 protein-positive Schwann cells, whereas a few CD34-positive fibroblastic cells were present in Antoni B areas. Neurofibromas and conventional MPNST exhibited a mixed proliferation of S-100 protein-, EMA/Glut1-, and CD34-positive cells, indicating a heterogeneous composition of the constituents. The catalyzed signal amplification (CSA) system demonstrated more numerous EMA-positive perineurial cells in neurofibromas than did the ENVISION+ method. Perineurial cell tumors (benign and malignant) were composed of EMA/Glut1-positive and S-100 protein-negative tumor cells. The present study confirmed the characteristic cellular composition to each nerve sheath tumor immunohistochemically and showed the usefulness of the nerve sheath cell markers. Glut1 as well as EMA are specific to perineurial cells, and CD34 seems to be immunoreactive to endoneurial fibroblasts.

Expression of claudin-1, a recently described tight junction-associated protein, distinguishes soft tissue perineurioma from potential mimics

Perineuriomas are rare benign soft tissue tumors having an immunophenotype paralleling the normal perineurial cell [S-100 protein negative and epithelial membrane antigen (EMA) positive]. Because EMA expression in perineuriomas may be focal and/or faint, there is continued interest in the development of new markers of perineurial differentiation. Perineurial cells differ from almost all other mesenchymal cell types by virtue of their formation of tight junctions. In the course of evaluating a group of novel tight junction-associated proteins, we noted high levels of expression of claudin-1 by normal perineurial cells and have systematically extended these observations to perineuriomas. Twelve EMA-positive/S-100-negative perineuriomas were retrieved from our consultation archives and compared with 39 tumors in the differential diagnosis of perineurioma (seven dermatofibrosarcoma protuberans, eight low-grade fibromyxoid sarcomas, three desmoplastic fibroblastomas, seven fibromatoses, nine neurofibromas, and five schwannomas). All cases were immunostained for claudin-1 using standard avidin-biotin technique. Cases were scored as 3+ (>50% positive cells), 2+ (25-50% positive cells), and 1+ (5-24% positive cells). In all cases positive internal controls in the form of epithelium, normal perineurium, or endothelial cells were present. Positive staining for claudin-1 was visualized in a distinctly particulate pattern along the cell membrane. Cytoplasmic staining was infrequent and was not scored as positive. Claudin-1 expression was present in 11 of 12 (92%) perineuriomas studied (seven at 3+, three at 2+, and one at 1+). In all but two cases, the degree of claudin expression was equal to or greater than the corresponding EMA immunostain. Claudin-1 expression was not noted in any cases of dermatofibrosarcoma protuberans, low-grade fibromyxoid sarcoma, desmoplastic fibroblastoma, or fibromatosis. Six of nine cases of neurofibroma contained a significant number of claudin-1-positive cells that were thought to be perineurial in origin, based on the staining of long, delicate cytoplasmic processes. One of four schwannomas contained a subpopulation of perivascular, dendritic, claudin-1-positive cells of presumed perineurial lineage. This is the first study to document expression of claudin-1 in perineurial cells and suggests a role for claudin-1 immunohistochemistry in the diagnosis of perineuriomas. Although claudin-1 should not replace EMA in the diagnosis of perineurioma, we think that it may play a valuable adjunctive role in difficult cases. In particular, claudin-1 is often a more robust marker than EMA in a given perineurioma. Claudin-1 is not expressed within the lesional cells of the mesenchymal tumors that enter into the differential diagnosis of perineurioma.

Leiomyosarcoma of the head and neck: a clinicopathological study

AIMS

The behaviour of leiomyosarcoma is site-related and there are few data on such tumours located in the head and neck. We studied the clinicopathological features of these lesions.

METHODS AND RESULTS

Cases diagnosed as leiomyosarcoma of the head and neck were retrieved from the archives of three institutions. Immunohistochemistry was performed and follow-up information was obtained. There were seven men and six women, aged 21-73 years, and lesions involved the neck (n=3), maxilla (n=4), buccal area (n=3), and maxillary sinus, nose, and pharynx (n=1 each). Tumours ranged from 10 to 80 mm. All tumours showed at least focally typical histological features of leiomyosarcoma with perpendicularly arranged fascicles of smooth muscle cells with blunt-ended nuclei, eosinophilic cytoplasm and paranuclear vacuoles. They expressed muscle-specific actin (8/9), smooth muscle actin (7/9), and desmin (10/12). Follow-up information was available on nine patients. All had surgery, with radiation and/or chemotherapy in seven. Three (27%) recurred at 6-24 months; in one case twice. Five (56%) had metastases, including the three with prior recurrences at 1-128 months. Five (including two who received adjuvant therapy) were disease-free at a median of 47 months, one was alive with metastatic disease at 24 months), and three were dead of disease (median 13 months).

CONCLUSIONS

Head and neck leiomyosarcomas are rare and aggressive neoplasms which metastasize. Adjuvant therapy has limited effect.

Diverse differentiation in malignant peripheral nerve sheath tumours associated with neurofibromatosis-1: an immunohistochemical and ultrastructural study

AIMS

The diverse histological features in malignant peripheral nerve sheath tumours (MPNSTs) associated with NF-1 were investigated by immunohistochemical and electron microscopic analysis. Our study is focused on the differentiation of the tumour cells in the heterogeneous components.

METHODS AND RESULTS

Twenty-three cases were classified as conventional type, epithelioid type, anaplastic type, and heterogeneous type, and divided into three groups by the presence of S100 protein (S100)-positive cells in each tumour; Group A was defined as having >50% S100+ cells, Group B as having <50%, and Group C as cases with no positive cells. To investigate the differentiation of the tumour cells, the morphology and immunoreactivity for neural or mesenchymal markers among the three groups were compared. For the identification of Schwannian, perineurial, and endoneurial differentiation, markers for S100, EMA and CD34 were used, respectively. In three tumours of the Group A type, there were no cases showing differentiation towards perineurial or endoneurial cells, or formation of heterogeneous components. In nine tumours of the Group B type, one tumour expressed EMA and CD34, suggesting probable perineurial and/or endoneurial differentiation. One tumour showed rhabdomyoblastic differentiation. Three tumours showed cartilaginous or osteogenic differentiation, and one of the three also showed a focal vascular differentiation. The surrounding areas of the heterogeneous components were composed of mixed S100+ cells and S100- cells. S100- cells in the areas were positive for CD34 in one case. In 11 tumours of Group C type, one tumour expressed EMA and CD34 suggesting perineurial and/or endoneurial cell differentiation. Three tumours showed rhabdomyoblastic differentiation. The tumour cells around the heterogeneous components in the three cases were negative for EMA and CD34.

CONCLUSION

Our results suggest that tumour cells differentiating to Schwann cells are not the only component of MPNSTs. Furthermore, tumour cells other than Schwann cells are largely related to the formation of the heterogeneous components in MPNSTs associated with NF-1.

Soft tissue sarcomas in the African hedgehog (Atelerix albiventris): microscopic and immunohistologic study of three cases

Three soft tissue tumors from 2 female hedgehogs were examined microscopically and immunohistochemically. Two tumors involved haired skin and the third one was vaginal. Microscopically, the cutaneous tumors had features of malignant peripheral nerve sheath tumor (MPNST), whereas the vaginal tumor was classified only as a spindle cell sarcoma. Immunohistochemically, all 3 tumors were strongly positive for vimentin and strongly to moderately positive for CD10 and neuron-specific enolase but did not stain with antibody to S100 protein, an antigen typically present in human MPNST The cutaneous tumor from hedgehog no. 1 was examined ultrastructurally and the neoplastic cells resembled fibroblasts. Hedgehog no. 1 was euthanized at the time of the biopsy. The outcome of the other hedgehog was unknown.

Dendritic cell neurofibroma with pseudorosettes: a report of 18 cases of a distinct and hitherto unrecognized neurofibroma variant

The authors present 18 cases of a hitherto unrecognized variant of cutaneous neurofibroma. The tumors presented in adults (10 occurred in men and eight occurred in women) as a solitary, well-circumscribed, superficial lesion located in the dermis measuring 3 to 17 mm (mean size, 6.2 mm). The tumors formed oval-shaped masses that ran perpendicular to the epidermis. In the deep part of the tumor there was multinodular arrangement with two types of cells: Type I cells were small, dark, lymphocyte-like cells with a slightly irregular nucleus and inconspicuous cytoplasm. Type II cells were larger, with pale-staining vesicular nuclei, with frequent invaginations and intranuclear inclusions, and had copious clear eosinophilic cytoplasm that formed a stellate growth pattern, which was poorly visible on hematoxylin and eosin staining. Type I cells were grouped concentrically around type II cells and formed pseudorosettes. Most of the type I and type II cells were S-100 protein and CD57 positive, and various proportions of both cell types were CD56 and PGP9.5 positive. All cells were chromogranin A, synaptophysin, glial fibrillary acidic protein, cytokeratins, CD1a, CD21, CD31, alpha-smooth muscle actin, muscle-specific actin, desmin, and HMB-45 negative. CD34 stained intralesional fibroblasts. Antibody to epithelial membrane antigen stained only the perineurium around the tumor masses, suggesting that the tumors arose inside the nerve sheath. No signs of neurosecretory granules were present at ultrastructural level. None of the lesions recurred and none metastasized over a mean follow-up of 8.1 years.

Myxoid variant of follicular dendritic cell sarcoma arising in the breast

Follicular dendritic cell sarcoma is a malignant tumor of the follicular dendritic cell which can arise in extranodal sites. We present here a case arising as a mass in the breast of a 41-year-old woman. The tumor was composed of mildly pleomorphic spindly cells with pale ovoid nuclei and cell processes intimately admixed with mature lymphocytes. In much of the lesion the cells were dispersed in cords in a myxoid stroma, and elsewhere there were solid sheets. The neoplastic cells were immunoreactive for CD21, CD35, EMA, and S100 protein, but not for other lymphoid markers or cytokeratin. Electron microscopy showed interdigitating cytoplasmic processes with junctions but no external lamina. The differential diagnosis includes carcinoma, lymphomas, and a variety of myxoid sarcomas. The tumor recurred within a few months and displayed increased nuclear pleomorphism and lymphatic invasion but the patient appears free of disease 3 years after the further excision. This case extends the spectrum of follicular dendritic cell sarcoma in soft tissue sites.

Malignant peripheral nerve sheath tumor of bone in children and adolescents

Malignant peripheral nerve sheath tumor (MPNST) of bone is a rare entity. We have examined three lesions that fit standard histopathologic criteria for MPNST of soft tissues but that arose in the skeleton of three children aged 6 to 13 years. None was affected by neurofibromatosis 1 (NF1). Histologic features typical of MPNST included spindle cells with comma-shaped nuclei, tactoid bodies, nuclear palisading, hyaline bands, and schwannoma-like and curlicue foci. Epithelioid foci were seen in two cases, and heterologous differentiation in one. Immunohistochemistry revealed positivity for S-100 (1 positive/3 tested), vimentin (3/3), glial fibrillary acidic protein (2/3), CD34 (1/1), and CD68 (1/2). Studies for CD99 (0/3), epithelial membrane antigen (0/3), cytokeratin (0/3), CD57 (0/3), and HMB-45 (0/2) were negative. Ultrastructural findings in one of two cases examined included interlacing, attenuated cytoplasmic processes, microtubules, and rare dense-core granules. We conclude that MPNST may arise as a primary bone neoplasm in children without NF1.

Poorly differentiated synovial sarcoma: an analysis of clinical, pathologic, and molecular genetic features

Poorly differentiated synovial sarcoma is a variant of synovial sarcoma in which the tumor cells lack the bland spindle cell appearance of the usual type monophasic synovial sarcoma. Although poorly differentiated synovial sarcoma has been recognized as an entity for many years, no series addressing the clinicopathologic features of this variant have appeared. We describe the histologic, immunohistologic, and molecular findings of a series of 20 poorly differentiated synovial sarcomas. Three types of poorly differentiated synovial sarcoma can be recognized: a large cell epithelioid variant, a small cell variant, and a high-grade spindle cell variant. Epithelial membrane antigen reactivity was seen in 95% of cases, and reactivity for cytokeratin was seen in 42%. The S100 antigen was expressed in 63% of cases. Electron microscopic findings in poorly differentiated synovial sarcoma parallel those found in usual type synovial sarcoma. In 10 cases, material was available for molecular studies; 9 of 10 cases showed the presence of t(X;18) or the associated fusion gene product. These data indicate that poorly differentiated synovial sarcoma is a lesion that shares immunologic, ultrastructural, and molecular characteristics with the usual synovial sarcoma. Follow-up data were available in 16 patients with a mean follow-up of 39 months. Eight patients died with a mean survival time of 33 months. Poorly differentiated synovial sarcoma is a variant of synovial sarcoma that may be associated with a poor prognosis.

Synovial sarcoma

Synovial sarcoma is a rare soft tissue tumor of children and adults that is unrelated to synovium and can occur in almost any part of the body. The familiar biphasic synovial sarcoma has discernible glandular or solid epithelial structures, and monophasic forms have characteristic ovoid or spindle cells with only immunohistochemical or ultrastructural evidence of epithelial differentiation. There are several morphologic patterns, including myxoid and hemangiopericytic, and behaviorally distinct calcifying, ossifying, and poorly differentiated subtypes can be recognized. Most synovial sarcomas are immunoreactive for cytokeratin, epithelial membrane antigen, and bc12 protein, and negative for CD34, and many express S100 protein and CD99 (MIC2). Nearly all synovial sarcomas have a specific t(x;18) (p11.2;q11.2) chromosomal abnormality, resulting in fusion of either of two variants of the SSX gene with the SYT gene; the genetic features may relate to morphology and outcome. The differential diagnosis can include a wide range of spindled, polygonal, or round cell sarcomas. Clinically, there have been marked recent improvements in local control of disease and lesser ones in management of metastases. The pathology, differential diagnosis, and behavior of this unique tumor are reviewed.

Perineurial malignant peripheral nerve sheath tumor (MPNST): a clinicopathologic, immunohistochemical, and ultrastructural study of seven cases

Most malignant peripheral nerve sheath tumors (MPNST) are schwannian in nature. The pathologic features of MPNST with perineurial cell differentiation remain to be characterized. To determine the clinicopathologic, immunohistochemical, and ultrastructural characteristics of perineurial MPNST, 121 MPNST from the Mayo Clinic Tissue Registry were examined. Of these 23 spindle cell tumors with long processes disposed in whorls or storiform patterns, features typical of perineurioma, were studied. On the basis of immunohistochemistry (epithelial membrane antigen+/S-100-), 5 perineurial MPNST were identified among 23 tumors selected. These and two previously characterized perineurial MPNST are the subject of this study. None of seven tumors was associated with NF-1. Patients included five males and two females ranging in age from 11 to 83 years (mean, 45.7 years). The tumors measured 1.5 to 30 cm (mean, 9.1 cm) and arose in the extremities (two), trunk (two), face (one), mediastinum (one), and retroperitoneum (one). Only one tumor was nerve associated (phrenic nerve). All tumors were surgically removed. No encapsulation or neurofibroma components were noted. Necrosis was seen in three lesions. Four tumors were classified as high-grade malignant and three as low grade. Mitotic indices varied from 1 to 85/10 high-power fields (median, 16). Immunoreactivities included epithelial membrane antigen (100%), vimentin (100%), Leu-7 (57%), and CD34 (14%). Stains for S-100 protein, muscle markers, and cytokeratin were nonreactive. Ultrastructurally, perineurial-like cells were noted in three tumors and cells intermediate between perineurial and Schwann cells in one. Four tumors recurred and two metastasized; no deaths of disease were noted at follow-ups of 28 to 98 months (mean, 66.9). In conclusion, 4% of MPNST show perineurial cell differentiation. An NF-1 association has yet to be described. Nerve involvement is infrequent. Their immunophenotype (epithelial membrane antigen+/S-100-) frequently indicates ultrastructural perineurial differentiation. The prognosis of perineural MPNST appears to be more favorable than that of conventional MPNST.

Poorly differentiated synovial sarcoma: immunohistochemical distinction from primitive neuroectodermal tumors and high-grade malignant peripheral nerve sheath tumors

Synovial sarcoma is a relatively common sarcoma in adults, which in its classic bimorphic form infrequently poses a diagnostic problem. Monomorphic spindled variants, as well as the less common poorly differentiated variants, may be confused with other soft-tissue sarcomas; the poorly differentiated variant (PDSS), in particular, may be histologically indistinguishable from other small, blue, round cell tumors, including primitive neuroectodermal tumors (PNETs). Detection of the synovial sarcoma-associated t(X;18) by either cytogenetic or molecular genetic approaches may be necessary to confirm the diagnosis of synovial sarcoma in difficult cases. We evaluated 10 cases of PDSS from eight patients using a panel of antibodies (including those to intermediate filament proteins, nerve-sheath associated markers, and neuronal and neuroectodermal associated markers) in order to better establish the immunophenotype of this tumor and to help distinguish it from the tumors with which it may be confused, particularly PNETs and high-grade malignant peripheral nerve sheath tumors (MPNSTs). Our results showed PDSS to have significant immunophenotypic overlap with both PNETs and MPNSTs. In most instances these three entities may be differentiated by a panel of antibodies that should include those to both low and high molecular weight cytokeratins, epithelial membrane antigen, type IV collagen, CD99, CD56, and S-100 protein. Our results also suggest that synovial sarcoma may be a tumor showing combined neuroectodermal and nerve sheath differentiation--perhaps because of translocation-associated expression of specific proteins--rather than a carcinosarcoma of soft tissues or a tumor of specialized arthrogenous mesenchyme.

Malignant peripheral nerve sheath tumor of the pancreas with perineurial cell differentiation

The authors report a malignant peripheral nerve sheath tumor (MPNST) that developed in the body of the pancreas of a 76-year-old woman. The well-demarcated tumor, 4.5 x 3.5 cm in size, was composed of spindle-shaped cells arranged in a storiform pattern or sweeping fascicles. Ultrastructurally, the tumor cells had elongated cytoplasmic processes with numerous pinocytotic vesicles, and were covered with discontinuous basal lamina-like substances. Immunohistochemically, tumor cells were diffusely positive for epithelial membrane antigen, vimentin, and CD34, but negative for S-100 protein and Leu 7. It was therefore concluded that the tumor was a MPNST with perineurial cell differentiation. Primary MPNST of the pancreas is extremely rare and the immunohistochemical and ultrastructural studies are necessary for its diagnosis.

Radiation-associated synovial sarcoma

We describe a case of synovial sarcoma occurring in a 36 year-old woman, 8 years after radiation therapy for Hodgkin's disease. The tumor showed histological, immunohistochemical, ultrastructural, and molecular features diagnostic of synovial sarcoma. To our knowledge, this is the first report of a fully documented case of radiation associated synovial sarcoma.

Pancreatic mucinous cystic neoplasm with sarcomatous stroma: a report of three cases

Three patients with pancreatic mucinous cystic neoplasms having a sarcomatous stroma are reported. The tumors occurred in two women and one man, aged 48, 66, and 67 years, respectively. Symptoms included epigastric pain or a palpable abdominal mass or both. Radiographically, all the tumors were large, multicystic, and located in the tail of the pancreas. Histologically, the cystic component was lined by mucin-producing, columnar to cuboidal epithelium composed of benign to atypical to overtly malignant cells (cystadenocarcinoma). Immunohistochemistry showed the epithelial component of all three tumors to be positive with cytokeratin, epithelial membrane antigen, carcinoembryonic antigen, and the pancreatic epithelial mucin antibodies CA 19-9 and DUPAN 2. In all three cases, an undifferentiated malignant spindle cell (sarcomatous) stroma was intimately associated with the epithelial component. The sarcomatous component showed variable reactivity with vimentin (all three cases), muscle-specific and smooth-muscle actin (all three cases), S-100 protein (1/3), Leu-7 (one case), and estrogen and progesterone receptors (in two cases). Two patients died with widespread abdominal disease within 15 months of diagnosis, one of whom had an omental metastasis entirely composed of the sarcomatous stroma. The third patient was alive and free of disease at 16 months after diagnosis. Our findings document the existence of a sarcomatous component in pancreatic mucinous cystic neoplasms; this component appears to be responsible for the highly malignant behavior of the tumors.

Ultrastructural heterogeneity of acquired intradermal melanocytic nevus cells

The present ultrastructural evaluation of 12 acquired intradermal melanocytic nevi revealed that in contrast to the nested epithelioid melanocytic nevus cells of the upper dermis, the spindle nevus cells of the deep dermis showed perineurial differentiation, exhibiting a spindly configuration characterized by a melanosome-free cytoplasm that showed extremely slender bipolar contour and contained abundant intermediate filaments, a decreased number of cytoplasmic organelles, and, significantly, a fair number of plasmalemmal pinocytotic vesicles. The nevic corpuscles were found to consist of laminated slender cytoplasm showing subcellular conformation similar to that of the spindle nevus cells. By immunohistochemistry, many spindle nevus cells and nevic corpuscles were immunoreactive for nerve growth factor receptor. All the nevus cells were immunoreactive for vimentin and S-100 protein, and negative for protein gene product 9.5, epithelial membrane antigen, Leu-7, and myelin basic protein. Characteristically, protein gene product 9.5 immunohistochemistry revealed numerous immunoreactive axons intermingled with the spindle nevus cells in the deep portion. All the PGP9.5-immunoreactive axons were observed by immunoelectron microscope to be unmyelinated and always ensheathed by a thin cytoplasmic process of Schwann cells but not nevus cells. These findings indicate that differentiation plasticity exists in the various nevus cells, with the epithelioid nevus cells and the spindle nevus cells displaying more ultrastructural and immunophenotypical characteristics of melanocyte and perineurial cells, respectively, suggesting that a pluripotential cell of neural crest origin accounts for the histogenesis of this lesion.

Radiation induced malignant schwannoma arising in a neurofibroma

Radiation induced sarcomas offer diagnostic and therapeutic challenges. The authors report an unusual case of radiation induced sarcoma arising 9 years after radiation therapy for chordoma. The location of this mass in the retroperitoneum and its intimate involvement with the spine raised difficult management issues. After limited resection was performed, consistent with the intraoperative diagnosis of a benign neurofibroma, foci of malignant transformation were found in areas of the specimen remote from the biopsy site. This complicated management of the sarcoma. The possibility of occult malignancy should be considered when evaluating tumors arising in a previously irradiated field. Thorough sampling at the time of biopsy is required to evaluate such lesions, particularly peripheral nerve sheath tumors.

Variability of differentiation patterns in xenotransplanted spindle cell sarcomas: a histomorphological, immunohistochemical, and ultrastructural study

Three leiomyosarcomas, 3 nerve sheath sarcomas, 1 rhabdomyosarcoma, and 1 sarcoma not otherwise classifiable with 17 of their xenografts, grown on nude mice, were analyzed to assess the degree of concordance between histomorphology, immunohistochemistry, and ultrastructure in spindle cell sarcoma xenograft differentiation. Histomorphology was inconclusive or misleading in 4/8 sarcoma strains and immunohistochemistry in 4/8 originals and in 10/17 xenografts, although specific patterns had been identified ultrastructurally. Electron microscopy was superior to immunohistochemistry and histomorphology in spindle cell sarcoma differential diagnosis. A further purpose of this study was to clarify whether spindle cell sarcoma xenografts retain the morphological characteristics of their primaries. Histomorphological features of the primaries were preserved over all passages, whereas the immunohistochemical marker profiles as well as the ultrastructural phenotypes changed in 14/17 xenografts and in 8/17 xenografts, respectively. Moreover, unusual bidirectional or tridirectional patterns of differentiation were identified ultrastructurally with leiomyomatous as well as Schwann cells occurring side by side and with MFH-like areas in 5/17 xenotransplants. These findings suggest genetic instability of tumor cells and may be important in the consideration of mesenchymal differentiation pathways.

Myofibrosarcoma of the head and neck in children

We have identified a distinctive malignant soft tissue neoplasm that occurred in the head and neck region of six children. Histologically, these neoplasms presented an array of features ranging from low-grade spindle cell to high-grade fibrohistiocytic histologies and often had myoid characteristics. Ultrastructural and immunohistochemical studies indicated that they contained neoplastic myofibroblasts that were variably positive for vimentin (4 positive/4 tested), alpha-smooth muscle actin (4/5), muscle-specific actin (5/5), desmin (2/5), and v-src protein substrate p80/85 (4/5). Three patients died of rapidly progressive unresectable local disease, one died of metastatic and local disease, and two are alive 13 months and 8 years after wide resection. We conclude that these neoplasms form a distinctive subset of pediatric soft tissue sarcomas that display an aggressive clinical behavior, typically with local recurrence, and exhibit features of myofibroblastic differentiation.

Cellular schwannoma. A clinicopathologic, DNA flow cytometric, and proliferation marker study of 70 patients

BACKGROUND

A clinicopathologic study of 70 cases of cellular schwannoma was performed to assess their distribution, response to therapy, and rate of recurrence relative to modern prognostic indicators.

METHODS

Seventy-one cellular schwannomas from 70 patients were retrieved from the files of the Mayo Clinic Tissue Registry. The significance of mitotic index, proliferative marker staining (proliferating cell nuclear antigen and MIB1), immunochemical p53 expression, and DNA ploidy were assessed relative to tumor behavior, particularly recurrence. All parameters were subject to statistical analysis (Student's t test).

RESULTS

Cellular schwannomas represented 4.6% of benign peripheral nerve tumors operated on at the Mayo Clinic. In 15% of the cases, an initial diagnosis of malignancy had been made. The median patient age was 47.7 years (range, 15-80 years) and the female-to-male ratio was 1.6:1. The principle tumor locations were the para- and intraspinal regions, including the sacrum (64%), extremities (25%), and intracranial space (8%). All tumors consisted primarily of hypercellular, compact, Antoni A tissue. Mitoses (< or = 4/10 hPF]) were observed in 71% of the cases. Foci of necrosis were noted in 11% of cases. Ultrastructural studies and immunohistochemistry clearly demonstrated features of schwannian differentiation. Surgery was the treatment in all cases. Excision was intralesional to gross total in the majority; total resection with wide margins was undertaken in three tumors, each of which had initially been considered malignant. Follow-up in 47 patients (67%) ranged from 1 to 29 years (mean, 7.7 years) and revealed recurrences in 11 patients (23.4%): no patient experienced metastasis or died of tumor. Although no correlation existed between recurrence and DNA ploidy, percent S-phase determinations, proliferation marker (PCNA, MIB1) staining, or the frequency of p53 immunoreactivity, a statistically significant correlation (P < 0.001) was observed, however, between recurrence and mitotic indices.

CONCLUSION

Proliferation indices, as defined by immunochemical analysis, are not useful predictors of recurrence in cellular schwannoma. In lesions not completely resected, tumor recurrence is significantly correlated with mitotic count. The significant overall frequency of recurrence in this series is attributable to a high proportion of intraspinal and intracranial tumors. Our study confirms the benign nature of cellular schwannoma and underscores the necessity of distinguishing them from malignant peripheral nerve sheath tumors, lesions that often require adjuvant therapy.

Ossifying fibromyxoid tumor of soft parts with stromal cyst formation and ribosome-lamella complexes

Ossifying fibromyxoid tumor of soft parts (OFMT) is a recently named soft tissue tumor of uncertain nature. A case is described that presented in a 13-year-old boy as a discrete mass in the muscles of the lower abdominal wall. Light microscopy showed, in addition to the typical features of this entity, microcysts formed by accumulations of the myxoid stroma. Bone formation was lacking. Tumor cells were strongly immunoreactive for vimentin and glial fibrillary acidic protein and weakly so for S-100 protein. A few cells stained for desmin and alpha-smooth muscle actin. Ultrastructurally, there were abundant, patternless cytoplasmic intermediate filaments; short, poorly interdigitating processes; and discontinuous segments of thick external lamina. In addition, several cells contained typical ribosome-lamella complexes in small groups. Ribosome-lamella complexes occur in neoplastic hematopoietic cells but are uncommon in solid tumors, particularly those affecting the soft tissues. These findings extend the range of appearances described for OFMT, which is added to the list of tumors in which ribosome-lamella complexes have been demonstrated. The balance of evidence suggests that OFMT may represent a peripheral nerve sheath tumor of low-grade malignancy, although the picture is incomplete.

Ossifying subcutaneous tumor with myofibroblastic differentiation: a variant of ossifying fibromyxoid tumor of soft parts?

Immunohistochemical, ultrastructural, and flow cytometric studies were performed on an ossifying soft-tissue tumor, presumed to be a variant of ossifying fibromyxoid tumor of soft parts, which was located in the subcutis of the left buttock of a 76 year old Japanese woman. Histologically, this was a benign-looking spindle, oval, or round cell lesion, having a fibrous capsule with a discontinuous rim of bone as seen in typical cases. However, this lesion was also characterized by a high degree of cellular proliferation in storiform and whorl arrangements, extensive ossification, osteoid and metaplastic bone formation and absence of myxoid features. In an immunohistochemical study using formalin-fixed, paraffin-embedded sections, many tumor cells expressed vimentin, S-100 protein, Leu-7, neuron specific enolase, and desmin. Ultrastructurally, this neoplasm consisted of fibroblast-like cells and myofibroblast-like cells. This tumor had an aneuploid DNA content. No recurrence has been observed for 16 months. These results suggest that the neoplastic cells may show the phenotypic expressions of myofibroblast and also osteogenic differentiation.

Ossifying fibromyxoid tumour of soft parts: immunohistochemical and ultrastructural analysis

Ossifying fibromyxoid tumour of soft parts is a recently described benign neoplasm which usually presents in soft tissue. The histogenesis or pattern of differentiation is a source of controversy. Thirteen cases are reported herein. All arose in adults, principally on the upper trunk or head and neck region. None recurred. All but one tumour showed a shell of lamellar bone, laid down by reactive osteoblasts, at the tumour-host interface. The characteristic laciform, glomoid and fascicular patterns, usually in combination, necessitate differential diagnosis from chondroid, smooth muscle and neural tumours especially. Immunohistochemistry revealed positivity for S-100 protein in 10/12, desmin in 7/10 and smooth muscle actin in 4/8. Ultrastructural examination of four cases revealed prominent intermediate filaments, without myofilamentous organization, and a discontinuous external lamina. Immunoelectronmicroscopy localized desmin positivity to the filamentous meshwork. Differentiation therefore appears to take the form of an incomplete neural and smooth muscle phenotype, without evidence of complete maturation.