Recognizing hidden phenotypes in sarcomas through the electron microscope

Differentiation along a distinct cell lineage can be identified either morphologically or with the adjunct of different ancillary techniques. While immunohistochemistry has progressively supplanted electron microscopy as the method of choice to characterize the phenotype of neoplastic cells in soft tissue tumors and in solving most differential diagnoses, a number of lesions still lack reliable specific markers or show overlapping antigen expression, which can be categorized by ultrastructural analysis through the recognition of submicroscopic features indicative of a specific line of differentiation. This review discusses the role of electron microscopy in the identification of the phenotype of neoplastic cells in soft tissue sarcomas, with particular reference to the diagnostic aspects. Sarcomas in which the cellular phenotype that can be better recognized by electron microscopy include those belonging to the fibroblastic/myofibroblastic group, particularly those displaying a poorly differentiated/pleomorphic morphology. Occasionally, in tumors with smooth muscle, skeletal muscle, adipocytic, vascular endothelial, and Schwann cell differentiation electron microscopy may help in the differential diagnosis.     

A Simple Procedure for Reducing Sampling Problems in the Transmission Electron Microscope Diagnosis of Human Tumors

A simple procedure is described which permits more extensive sampling in the transmission electron microscopic analysis of human tumor tissue. Thin slices of 2 to 4 mm side are cut from fresh or fixed specimens and processed for embedding in exactly the same manner as for conventional mm-cubes pieces, with blocking out in 8 mm-diameter flat-bottomed molds. Advantages and shortcomings of the technique compared with other published methods having the same objective, are discussed. Examples are given to illustrate the usefulness of the procedure.     

A Simple Procedure for Reducing Sampling Problems in the Transmission Electron Microscope Diagnosis of Human Tumors

A simple procedure is described which permits more extensive sampling in the transmission electron microscopic analysis of human tumor tissue. Thin slices of 2 to 4 mm side are cut from fresh or fixed specimens and processed for embedding in exactly the same manner as for conventional mm-cubes pieces, with blocking out in 8 mm-diameter flat-bottomed molds. Advantages and shortcomings of the technique compared with other published methods having the same objective, are discussed. Examples are given to illustrate the usefulness of the procedure.     

Fine-needle aspiration cytology of sarcoma: Retrospective review of diagnostic utility and specificity

Fine-needle aspiration cytology (FNA) is useful because of its low cost, quick turn around time, and low incidence of complications. This study investigates the role FNA plays in the evaluation of sarcoma. We reviewed all the pathologic material from patients with sarcoma or a FNA diagnosis suggestive of sarcoma at the University of California-Davis Medical Center (1985–1994). Fifty-two of 196 patients identified (26.5%) were evaluated with FNA exhibiting 46 soft tissue and 6 bone lesions located in the extremities (19), trunk (19), head and neck (8), retroperitoneum (3), and abdominal cavity (3). Among 196 patients identified, those evaluated by FNA had soft tissue rather than bone lesions (P < .001) and primary sites other than in the extremities (P < .001). The primary neoplasms for the 52 FNA patients included 47 sarcomas (10 malignant fibrous histiocytomas and 16 other types), I intramuscular myxoma, 2 lymphomas, and 2 spindle cell (sarcomatoid) carcinomas. In 43 patients (22% of total), FNA was used first, before a primary diagnosis. The FNA report showed the correct specific neoplasm in only 20.9%. However, the FNA reports reflected an effective positive diagnosis leading to appropriate diagnostic biopsy in 88.4%, while only 7.0% were misleading (benign or inflammatory) and 4.6% inadequate. Review of FNA slides for 32 of 43 patients in which FNA was used first, in a blinded fashion, exhibited 21.9% specificity for the specific neoplasm, and 88.4% effective positive diagnoses. In 9 patients, FNA was utilized to investigate recurrence. Five out of 5 instances of recurrent sarcoma were identified by FNA. However, FNA misidentified recurrence in 3/4 instances, exhibiting suspicious cells from regenerating skeletal muscle (2) and a traumatic neuroma (I). The specific diagnosis for sarcomas is challenging even with surgical material. FNA usually does not provide a specific diagnosis (only in 20.9% of cases) and review of routinely prepared slides showed the same specificity as reflected by the original FNA report, at times formulated with the benefit of immunohistochemistry or electron microscopy. FNA effectively evaluated lesions in 45 of 52 patients (86.5%), confirming the useful screening role for this technique in sarcomas. Diagn Cytopathol 1996;15:23–32. © 1996 Wiley-Liss, Inc.     

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

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

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

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

Role of electron microscopy in the evaluation of soft tissue neoplasms, with emphasis on spindle cell and pleomorphic tumors

The current significant role of transmission electron microscopy in the evaluation of soft tissue tumors when correlated with conventional histological and immunohistochemical studies is discussed for the following entities: myxofibrosarcoma, storiform-pleomorphic fibrosarcoma (malignant fibrous histiocytoma), and myofibrosarcoma; dermatofibrosarcoma protuberans; hemangiopericytoma; monophasic synovial sarcoma; extrarenal rhabdoid tumor; soft tissue perineurioma; and gastrointestinal stromal tumors, notably the so-called autonomic nerve variant.     

Chordomalike Soft Tissue Sarcoma in the Leg: A Light and Electron Microscopic and Immunohistochemical Study

A soft tissue tumor in the leg of a 67-year-old woman is described. This large tumor below the knee area infiltrated extensively the deep and superficial soft tissues but did not involve the bones. The tumor cells formed nodules resembling the architecture seen in chondroid tumors and chordoma. The tumor cells were often vacuolized, and there was extracellular myxoid matrix similar to that in chordoma or myxoid chondrosarcoma. Immunohistochemistry showed keratins 8 and 19, epithelial membrane antigen, and vimentin in most tumor cells, and there was also S-100 protein positivity in a number of tumor cells. Electron microscopy showed desmosomelike cell junctions and bundles of intermediate filaments resembling those seen in many epithelial neoplasms. Thus the tumor resembled chordoma in many respects. Because clinically no other primary tumor was found, this tumor is probably a chordomalike primary soft tissue sarcoma different from typical extraskeletal myxoid chondrosarcoma or chordoid sarcoma.     

Chordomalike Soft Tissue Sarcoma in the Leg: A Light and Electron Microscopic and Immunohistochemical Study

A soft tissue tumor in the leg of a 67-year-old woman is described. This large tumor below the knee area infiltrated extensively the deep and superficial soft tissues but did not involve the bones. The tumor cells formed nodules resembling the architecture seen in chondroid tumors and chordoma. The tumor cells were often vacuolized, and there was extracellular myxoid matrix similar to that in chordoma or myxoid chondrosarcoma. Immunohistochemistry showed keratins 8 and 19, epithelial membrane antigen, and vimentin in most tumor cells, and there was also S-100 protein positivity in a number of tumor cells. Electron microscopy showed desmosomelike cell junctions and bundles of intermediate filaments resembling those seen in many epithelial neoplasms. Thus the tumor resembled chordoma in many respects. Because clinically no other primary tumor was found, this tumor is probably a chordomalike primary soft tissue sarcoma different from typical extraskeletal myxoid chondrosarcoma or chordoid sarcoma.     

Pleomorphic hyalinizing angiectatic tumor of soft parts: ultrastructural analysis of a case with original features

Pleomorphic hyalinizing angiectatic tumor, a rare neoplasm of uncertain lineage resembling malignant fibrous histiocytoma and schwannoma, was first described in 1996 by M. E. F. Smith et al. (Am Surg Pathol. 20:21-29). To date, less than 100 cases have been reported in the international literature. It occurs in subcutaneous and intramuscular soft tissues of extremities or trunk in adults without sex predilection. All lesions are composed of sheets and fascicles of spindled and pleomorphic cells associated with clusters of thick-walled ectatic vessels surrounded by a perivascular hyaline material and inflammatory cells such as mast cells. About one-half of these neoplasms express CD34. No patient has developed metastases but occasional local recurrences are possible. This tumor of uncertain lineage is suggested to be an aggressive locally growing low-grade sarcoma. Only 3 cases were previously studied by electron microscopy and appeared to consist of primitive fibroblastic cells. The authors report histological and ultrastructural characteristics of a new case of PHAT excised from the right buttock of a 66-year-old man with the presence of ganglion-like cells, a feature that has not been previously reported, and unusual central ischemic necrosis. The features of this case are suggestive of a fibroblastic origin.     

Pleomorphic Hyalinizing Angiectatic Tumor of Soft Parts: Ultrastructural Analysis of a Case with Original Features

Pleomorphic hyalinizing angiectatic tumor, a rare neoplasm of uncertain lineage resembling malignant fibrous histiocytoma and schwannoma, was first described in 1996 by M. E. F. Smith et al. (Am Surg Pathol. 20:21–29). To date, less than 100 cases have been reported in the international literature. It occurs in subcutaneous and intramuscular soft tissues of extremities or trunk in adults without sex predilection. All lesions are composed of sheets and fascicles of spindled and pleomorphic cells associated with clusters of thick-walled ectatic vessels surrounded by a perivascular hyaline material and inflammatory cells such as mast cells. About one-half of these neoplasms express CD34. No patient has developed metastases but occasional local recurrences are possible. This tumor of uncertain lineage is suggested to be an aggressive locally growing low-grade sarcoma. Only 3 cases were previously studied by electron microscopy and appeared to consist of primitive fibroblastic cells. The authors report histological and ultrastructural characteristics of a new case of PHAT excised from the right buttock of a 66-year-old man with the presence of ganglion-like cells, a feature that has not been previously reported, and unusual central ischemic necrosis. The features of this case are suggestive of a fibroblastic origin.     

A Role for Electron Microscopy in Salivary Gland Neoplasms

Undoubtedly, electron microscopy has a specific role to play in the diagnosis of a select group of salivary gland neoplasms. However, this tool has a current central role, along with immunohistochemical techniques, in elucidating morphogenetic processes in salivary gland tumors. New information gained from ultrastructural surveys of these tumors can be applied to improving classification and the diagnostic problems that are not infrequent for the surgical pathologist with salivary gland lesions.     

A Role for Electron Microscopy in Salivary Gland Neoplasms

Undoubtedly, electron microscopy has a specific role to play in the diagnosis of a select group of salivary gland neoplasms. However, this tool has a current central role, along with immunohistochemical techniques, in elucidating morphogenetic processes in salivary gland tumors. New information gained from ultrastructural surveys of these tumors can be applied to improving classification and the diagnostic problems that are not infrequent for the surgical pathologist with salivary gland lesions.     

Simple Technique to Facilitate Tissue Sampling for Electron Microscopy

The need to examine certain components of a specimen with the electron microscope is frequently recognized only after study of the paraffin sections, by which time the total specimen has usually been fixed in Formalin. Such specimens are frequently large, with the result that representative samples for electron microscopy may be difficult to isolate. A simple, quick, and inexpensive method for overcoming this sampling problem is described. This technique is best employed in laboratories that routinely use a single tissue fixative suitable for both light and electron microscopy. The specimen is taken direct from the Formalin, and very thin slices are prepared by hand with a blade, stained with methylene blue, and examined in the wet state under the microscope. On identification, representative tissue is removed by microdissection and processed further for electron microscopy.     

Simple Technique to Facilitate Tissue Sampling for Electron Microscopy

The need to examine certain components of a specimen with the electron microscope is frequently recognized only after study of the paraffin sections, by which time the total specimen has usually been fixed in Formalin. Such specimens are frequently large, with the result that representative samples for electron microscopy may be difficult to isolate. A simple, quick, and inexpensive method for overcoming this sampling problem is described. This technique is best employed in laboratories that routinely use a single tissue fixative suitable for both light and electron microscopy. The specimen is taken direct from the Formalin. and very thin slices are prepared by hand with a blade, stained with methylene blue, and examined in the wet state under the microscope. On identification, representative tissue is removed by microdissection and processed further for electron microscopy.     

Scanning Electron Microscope Characterization of Erosive Enamel in Human Teeth

This study aimed to examine the surface characteristics of erosive enamel in extracted human teeth by scanning electron microscopy. Morphologic changes in naturally eroded enamel depend on the stages of dental erosion. In its early stages, the enamel surfaces show a honeycomb appearance due to the dissolution of enamel rod ends. In its advanced stages, the erosive process involves the underlying dentin and the eroded dentin shows exposed dentinal tubules and the dentinal matrix may be exposed due to the dissolution of the peri- and intertubular dentin. Evidence of remineralization is seen at the early stage of natural dental erosion.     

Malignant granular cell tumors: the role of electron microscopy in the definitive diagnosis of an extremely aggressive soft tissue neoplasm

Granular cell tumors (GCTs) are rare soft tissue neoplasms which may be multicentric. The vast majority are benign, however approximately 100 malignant GCTs have been reported, with only 8 originating in the vulva. Malignant GCTs are very aggressive with very poor survival rates. As the diagnosis of malignant GCT carries an extremely poor prognosis, the utilization of EM ensures that the most accurate diagnosis possible can be rendered.     

The Evolving Concept of Renal Neoplasia: Impact of Emerging Molecular and Electron Microscopic Studies

The classification of renal tumors has evolved from one that initially encompassed only 2 types of tumors, i.e., clear and granular cell carcinomas, to the markedly expanded recent classification that incorporates new entities, some of which are primarily defined by specific molecular abnormalities. Despite these advances, a single tumor category, clear cell carcinoma, still incorporates the majority (∼70%) of renal tumors. It is, however, postulated that this single category is likely to encompass several different tumor types that are, at present, undifferentiated. Electron microscopic studies have been pivotal in defining the spectrum of oncocytoma-chromophobe renal cell carcinoma. Cytoplasmic eosinophilia found in some renal cell carcinomas currently classified as clear cell type is under intense study. Tumors that have recently emerged from this group include tumors with translocations involving chromosome Xp11.2, carcinomas associated with neuroblastoma and epithelioid angiomyolipoma. The spectrum of renal tumors seen in younger patients is wider than among older patients, with rare and unusual tumors being more likely seen in younger patients. The author concludes that although the routine application of electron microscopy to kidney tumor diagnosis may not be practical, systematic ultrastructural studies of these tumors may aid in the definition of new entities.     

The Evolving Concept of Renal Neoplasia: Impact of Emerging Molecular and Electron Microscopic Studies

The classification of renal tumors has evolved from one that initially encompassed only 2 types of tumors, i.e., clear and granular cell carcinomas, to the markedly expanded recent classification that incorporates new entities, some of which are primarily defined by specific molecular abnormalities. Despite these advances, a single tumor category, clear cell carcinoma, still incorporates the majority (～70%) of renal tumors. It is, however, postulated that this single category is likely to encompass several different tumor types that are, at present, undifferentiated. Electron microscopic studies have been pivotal in defining the spectrum of oncocytoma–chromophobe renal cell carcinoma. Cytoplasmic eosinophilia found in some renal cell carcinomas currently classified as clear cell type is under intense study. Tumors that have recently emerged from this group include tumors with translocations involving chromosome Xp11.2, carcinomas associated with neuroblastoma and epithelioid angiomyolipoma. The spectrum of renal tumors seen in younger patients is wider than among older patients, with rare and unusual tumors being more likely seen in younger patients. The author concludes that although the routine application of electron microscopy to kidney tumor diagnosis may not be practical, systematic ultrastructural studies of these tumors may aid in the definition of new entities.     

Myofibroblastoma of the Axilla

A mass in the axilla of a 47-year-old woman was biopsied and resected. The mass was composed of a loosely distributed population of spindle cells that were immunoreactive for smooth-muscle actin. Ultrastructurally, the cells possessed abundant endoplasmic reticulum, and some contained peripheral smooth muscle myofilaments, establishing that they were myofibroblasts. Mitotic activity was sparse, there was no cytologic atypia, and by flow cytometry the tumor was diploid with a low S phase. A diagnosis of myofibroblastoma was favored, although the possibility of a low-grade sarcoma could not be excluded. There has not been any indication of recurrence over a 4-month period of follow-up.