The ultrastructure of poorly differentiated rhabdomyosarcomas: a case report and literature review

On the Origin of ATP Synthesis in Cancer

ATP is required for mammalian cells to remain viable and to perform genetically programmed functions. Maintenance of the ΔG′_ATP hydrolysis of −56 kJ/mole is the endpoint of both genetic and metabolic processes required for life. Various anomalies in mitochondrial structure and function prevent maximal ATP synthesis through OxPhos in cancer cells. Little ATP synthesis would occur through glycolysis in cancer cells that express the dimeric form of pyruvate kinase M2. Mitochondrial substrate level phosphorylation (mSLP) in the glutamine-driven glutaminolysis pathway, substantiated by the succinate-CoA ligase reaction in the TCA cycle, can partially compensate for reduced ATP synthesis through both OxPhos and glycolysis. A protracted insufficiency of OxPhos coupled with elevated glycolysis and an auxiliary, fully operational mSLP, would cause a cell to enter its default state of unbridled proliferation with consequent dedifferentiation and apoptotic resistance, i.e., cancer. The simultaneous restriction of glucose and glutamine offers a therapeutic strategy for managing cancer.

Primary cilia control hedgehog signaling during muscle differentiation and are deregulated in rhabdomyosarcoma

The primary cilium acts as a cellular antenna, transducing diverse signaling pathways, and recent evidence suggests that primary cilia are important in development and cancer. However, a role for cilia in normal muscle development and rhabdomyosarcoma (RMS) has not been explored. Here we implicate primary cilia in proliferation, hedgehog (Hh) signaling, and differentiation of skeletal muscle cells. Cilia and Hh signaling are highly dynamic during the differentiation of myoblasts. We show that cilia are assembled during the initial stages of myogenic differentiation but disappear as cells progress through myogenesis, concomitant with the destruction of proteins critical for cilia assembly and shortly after the Hh effector, Gli3, leaves the cilium. Importantly, we show that ablation of primary cilia strongly suppresses Hh signaling and myogenic differentiation while enhancing proliferation. Interestingly, our data further indicate that both cilia assembly and Hh signaling are deregulated in RMS, and cilia respond to Hh ligand in certain subsets of RMS cells but not others. Together, these findings provide evidence for an essential role for both primary cilia assembly and disassembly in the control of Hh signaling and early differentiation in muscle cells. We suggest that the temporally orchestrated destruction of centrosomal and ciliary proteins is a necessary antecedent for removal of the primary cilium and cessation of Hh signaling during myogenic differentiation. Additionally, our results further stratify RMS populations and highlight cilia assembly and disassembly as potential RMS drug targets.

A Comparative Review of Canine and Human Rhabdomyosarcoma With Emphasis on Classification and Pathogenesis

Rhabdomyosarcomas are a diverse group of malignant mesenchymal neoplasms exhibiting variable levels of differentiation toward skeletal myocytes. Neoplastic cells may resemble relatively undifferentiated myoblasts, satellite cells, or more differentiated elongated spindle cells and multicellular myotubes. In veterinary medicine, classification into subtypes and variants is based on an outdated system derived from human pathology and is solely based on histologic characteristics. In contrast, classification of human rhabdomyosarcoma is based on histologic, immunohistochemical, and molecular diagnostic techniques, and subclassification has clinical and prognostic relevance. Relevance of tumor subtyping has not been established in veterinary medicine. Recent discoveries of components of the molecular pathogenesis and genomes of human rhabdomyosarcomas have led to new diagnostic techniques and revisions of the human classification system. The current classification system in veterinary medicine is reviewed in light of these changes. Diagnosis of rhabdomyosarcoma using histopathology, electron microscopy, and the clinical aspects of human and canine rhabdomyosarcomas is compared. The clinical features and biologic behavior of canine rhabdomyosarcomas are compared with canine soft tissue sarcomas.

Pleomorphic rhabdomyosarcoma showing smooth-muscle and fibrohistiocytic differentiation: a single case report

Rhabdomyosarcoma has traditionally been subclassified into alveolar, embryonal, and pleomorphic variants. Less commonly, spindle-cell, neuroendocrine, sclerosing, and lipid-rich or clear-cell subtypes are seen. The author recently encountered a myogenic sarcoma, with all the common markers of rhabdomyosarcoma, but expressing the unusual features of alpha-smooth-muscle actin and abundant rough endoplasmic reticulum (rER). This myogenic sarcoma, therefore, exhibited four lines of differentiation, and is documented here. The patient was a 65-year-old man with an inguinal soft tissue mass. Following surgical excision, the patient was given radiotherapy and was well without disease after 6 years. The tumor was positive for vimentin, desmin, alpha-smooth-muscle actin, alpha-sarcomeric actin, myogenin, MyoD1, and CD68. Cytoplasm was dominated by abundant rER intermingled with lipid droplets and lysosomes. Cell surfaces exhibited microvillous processes and focal adhesions, but no lamina. Subplasmalemmal smooth-muscle-type myofilaments with focal densities and rare sarcomeric filaments were seen. The low level of expression of some markers was interpreted as consistent with a poorly differentiated tumor. Given the four lines of differentiation--striated muscle, smooth muscle, fibroblastic, and histiocytic--a name reflecting its phenotype would be pleomorphic rhabdomyosarcoma showing smooth-muscle and fibrohistiocytic differentiation.

A case of leiomyosarcoma of the sphenoid sinus

A 43-year-old man with a primary leiomyosarcoma of the left sphenoid sinus is presented. To our knowledge, this is an unusual case of leiomyosarcoma, which has never been reported in the literature. Accurate and safe diagnosis was obtained by an endonasal endoscopic approach with minimal tissue invasion.

Gastric stump carcinosarcoma with rhabdomyosarcomatous differentiation

Gastric carcinosarcoma is an unusual tumor and its occurrence in the gastric stump is extremely rare. A report is presented here of a unique case of gastric stump carcinosarcoma with rhabdomyosarcomatous differentiation in a 74-year-old man. The patient had undergone partial gastrectomy with gastrojejunostomy (Billroth II method) 30 years previously. The tumor had both adenocarcinoma and sarcoma components, and an immunohistochemical study suggested a focal transition between these components. The main sarcomatous components showed fibrosarcomatous features with a scattered distribution of rounded tumor cells, whose rhabdomyosarcomatous differentiation was immunohistochemically determined. Ultrastructural examination supported the rhabdomyosarcomatous natures. Experience with the present tumor indicates that carcinosarcoma with rhabdomyosarcomatous differentiation can occur in the gastric stump and that this disease is capable of aggressive behavior.

Classification of rhabdomyosarcomas and related sarcomas. Pathologic aspects and proposal for a new classification--an Intergroup Rhabdomyosarcoma Study

BACKGROUND

There is a need to develop a single prognostically significant classification of rhabdomyosarcomas (RMS) and other related tumors of children, adolescents, and young adults which would be a current guide for their diagnosis, allow valid comparison of outcomes between protocols carried out anywhere in the world, and should enhance recognition of prognostic subsets.

METHOD

Sixteen pathologists from eight pathology groups, representing six countries and several cooperative groups, classified by four histopathologic classification schemes 800 representative tumors of the 999 eligible cases treated on Intergroup Rhabdomyosarcoma Study II. Each tumor was classified according to each of the four systems by each of the pathologists. In addition, two independent subsamples of 200 of the 800 patients were reviewed according to the new system, so that 343 distinct patients were reviewed once, and 57 of these twice.

RESULTS

A study of the survival rates of all subtypes in the sample of 800 patients led to the formation of a new system. This was tested on two independent subsets of 200 of the original cases and found to be reproducible and predictive of outcome by univariate analysis. A multivariate analysis of the 343 patients classified according to the new system indicated that a survival model including pathologic classification and known prognostic factors of primary site, clinical group, and tumor size was significantly better at predicting survival than a model with only the known prognostic factors.

CONCLUSION

This new classification, termed International Classification of Rhabdomyosarcoma (ICR) by the authors, was reproducible and predictive of outcome among patients with differing histologies treated uniformly on the Intergroup Rhabdomyosarcoma II protocols. We believe it should be utilized by all pathologists and cooperative groups to classify rhabdomyosarcomas in order to provide comparability among and within multi-institutional studies.

The expression pattern of contractile and intermediate filament proteins in developing skeletal muscle and rhabdomyosarcoma of childhood: diagnostic and prognostic utility

In order to investigate whether rhabdomyosarcoma (RMS) can be related to equivalent stages of skeletal muscle development, muscle tissue of 21 human foetuses and 112 primary RMSs were characterized immunohistochemically using antibodies directed against vimentin, desmin, muscle-specific actin (HHF35), sarcomeric actin (sr-actin), smooth muscle actin (sm-actin), and troponin-T. During fetal skeletal muscle development, all myotubes/fibres of the first and second generations expressed desmin, HHF35, and sr-actin. Vimentin was almost exclusively present in immature primary and secondary myotubes/fibres. Troponin-T was expressed in immature myotubes/fibres of the first and second generations as well as mature fibres of the second generation. Sm-actin was never expressed. Vimentin was expressed in 96 per cent of primary and 98 per cent of relapsed RMS; HHF35 in 96 and 98 per cent, respectively; desmin in 95 and 100 per cent; troponin-T in 82 and 75 per cent; sr-actin in 71 and 86 per cent; and sm-actin in 13 and 17 per cent. The proportion of RMS cells reacting with vimentin, HHF35, and desmin was consistently higher than those expressing sr-actin and troponin-T. Neither the shape nor size of neoplastic RMS cells nor the histopathological types were related to the expression pattern of the investigated markers. RMS with aberrant expression of two or more markers predicted a worse prognosis than RMS in which at most one marker was aberrantly expressed (25 per cent and 54 per cent 10-year survival, P = 0.01). These results demonstrate that HHF35, desmin, sr-actin, and troponin-T have the potential to confirm the commitment of the tumours to the myogenic pathway which supports the diagnosis of RMS. However, it was impossible to relate RMS to equivalent stages of skeletal muscle development. Aberrant marker expression by RMS cells correlated significantly with patients' survival.

Lipid rich rhabdomyosarcoma

A lipid rich rhabdomyosarcoma of the paratesticular region was studied by light microscopy, histochemistry, immunohistochemistry and electron microscopy. The tumour was composed of primitive looking, vacuolated, and pleomorphic cells. Lipid was present in varying amounts in all cells but was especially abundant in the vacuolated and pleomorphic cells. Some cells showed eosinophilic fibrillary cytoplasm but cross-striations were not seen. Tumour cells were positive for desmin, muscle specific actin, and vimentin. A few cells were myoglobin positive. At electron microscopy, the presence of lipid was confirmed, while thick and thin filaments, Z disks, lamina and glycogen were observed, thereby confirming striated muscle differentiation. Although moderate amounts of lipid can be expected in almost any tumour, lipid rich rhabdomyosarcomas have received little attention. The present report provides a comprehensively examined case of such a tumour initially presenting diagnostic difficulty because of its possible confusion with liposarcoma.

Embryonal rhabdomyosarcoma arising in the buccal mucosa: a case report with immunohistochemical and electronmicroscopic findings

Rhabdomyosarcoma is one of the most common soft-tissue neoplasms in children. We report a case of a 9-year-old female with embryonal rhabdomyosarcoma arising in the buccal region with immunohistochemical and electronmicroscopic findings. Under a light microscope, it was observed that the tumor was composed of small round or spindle-shaped cells with pleomorphic and hyperchromatic nuclei. They were immunoreactive for actin, myoglobin and desmin. With an electron microscope, it was found that most tumor cells contained filamentous structures and free ribosomes. Some of them showed typical myofilaments, M-bands and Z-lines. These findings were specific evidence of rhabdomyosarcoma. Twenty courses of VAC (vincristine, D-actinomycin and cyclophosphamide) chemotherapy were administered, followed by surgical resection of the tumor.

Ultrastructural characterization of poorly differentiated rhabdomyosarcomas

Twenty-five rhabdomyosarcomas, histopathologically and immunocytochemically classified as embryonal (12 cases), alveolar (11 cases), and pleomorphic (two cases), were studied by routine and immunogold electron microscopy, to identify, in poorly differentiated cells, reproducible markers useful for diagnostic purposes. Rhabdomyoblasts with rudimentary sarcomeres were observed in 12 cases (48%). Large cells (named oval cells) with an oval shape and an eccentric nucleus, like rhabdomyoblasts but lacking organized myofilaments, were observed in 20 cases (80%). By immunogold electron microscopy, performed on four of 25 cases, both oval cells and rhabdomyoblasts showed abundant intermediate filaments positive for desmin. Oval cells may be used as markers of poorly differentiated rhabdomyosarcomas.

Infantile cutaneous rhabdomyosarcoma (Li-Fraumeni syndrome): cytological presentation of fine-needle aspirate biopsy, report of a case

We describe the cytopathological picture of a cutaneous rhabdomyosarcoma located in the left nasal furrow of a 4-mo-old girl, some of whose close relatives have died or suffered from different types of neoplasias (Li-Fraumeni syndrome). We believe that the cytological picture is highly characteristic and rules out other round cell tumours of childhood. We underline the usefulness of FNAC in dermatology and strongly advocate the introduction of this technique into the diagnostic armoury of every dermatologist.

Lipid-rich rhabdomyosarcoma--a potential source of diagnostic confusion

Rhabdomyosarcoma is an often primitive tumor capable of diverse morphologic manifestations. The article describes three cases of childhood rhabdomyosarcoma in which a significant population of lipid-rich tumor cells was present. The lack of specificity and potentially confusing nature of this feature are discussed, and the ultrastructural diagnosis of rhabdomyosarcoma is briefly reviewed.

The value of electronmicroscopy and immunohistochemistry in the diagnosis of soft tissue sarcomas: a study of 200 cases

Two hundred soft tissue sarcomas, accrued consecutively over a 4-year period, were examined by light and electronmicroscopy and by routine immunohistochemistry. The commonest tumour type was malignant fibrous histiocytoma. Fibrosarcoma, composed only of fibroblasts, was diagnosed in only one case; three others, composed also of myofibroblasts, could be regarded as fibrosarcomas or myofibrosarcomas. Immunohistochemistry was of most value in the diagnosis of rhabdomyosarcoma, leiomyosarcoma, malignant peripheral nerve sheath tumour of Schwann cell type and epithelioid sarcoma. Electronmicroscopy was of most use for the diagnosis of malignant peripheral nerve sheath tumour of perineurial cell type and marker-negative monophasic synovial sarcoma, and for confirming malignant fibrous histiocytoma. Fifteen of 19 marker-negative spindle cell tumours (79%) were diagnosable by electronmicroscopy. A combination of techniques resulted in a specific diagnosis in 193 cases (96.5%). The routine use of electronmicroscopy in sarcoma diagnosis can improve accuracy of diagnosis, establish the true frequency of marker-positivity for each ultrastructurally confirmed tumour type and minimise the number of unclassifiable cases.

Diffuse pleural rhabdomyosarcoma with persistent pleural effusion

A unique case of embryonal rhabdomyosarcoma arising at the left pleura of a 7-year-old Japanese girl is reported. The present case was characterized by persistent pleural effusion, and the malignant cells incidentally found in it were the first diagnostic clue. The tumor showed a rare growth pattern involving diffuse thickening of the parietal pleura. Biopsy of the thickened parietal pleura upon thoracotomy revealed embryonal rhabdomyosarcoma largely composed of immature mesenchymal cells. Immunohistochemical demonstration of creatinine phosphokinase-MM was most helpful among several types of immunostain for the histopathological diagnosis. Ultrastructurally, thin filaments with primitive Z bands could be seen in some tumor cells. Intensive clinical examination revealed only diffuse thickening of the parietal pleura, which was reduced by chemotherapy. This is the first documented case of rhabdomyosarcoma arising at the pleura. Previous reports of rhabdomyosarcoma arising at unusual sites are reviewed and the histogenesis of this tumor is briefly discussed.

Laryngeal botryoid rhabdomyosarcoma in an adult. Report of a case with electron microscopic study

Light and electron microscopic studies of botryoid rhabdomyosarcoma of the larynx in an adult are presented. Differences in cellular composition of the central and peripheral regions of the tumor are described. The ultrastructure of the rhabdomyoblasts is discussed on the basis of criteria recently described. The findings support the hypothesis that botryoid rhabdomyosarcoma is a special subtype of rhabdomyosarcoma with low grade malignancy.

Rhabdomyosarcoma in children: a histological and immunohistochemical study of 59 cases

Recent studies have suggested that rhabdomyosarcoma can be divided into favourable and unfavourable histology groups. Those subtypes comprising the unfavourable histology group are alveolar, monomorphous round cell and anaplastic rhabdomyosarcoma, with a favourable histology group of embryonal rhabdomyosarcomas. An immunohistological study was undertaken on 59 childhood rhabdomyosarcomas, using antisera to keratin, S100 protein, vimentin, desmin, myoglobin, and troponin T. Our results suggest that desmin is the single most useful antibody in the diagnosis of rhabdomyosarcoma and was expressed in all our cases. The expression of troponin T in the majority of embryonal rhabdomyosarcomas but not in the other histological types has prognostic implications.

Fine-needle aspiration biopsy of clear-cell sarcoma of the kidney: light and electron microscopic features

Smears from seven fine-needle aspiration biopsies from three patients with clear-cell sarcoma of the kidney were reviewed, and the findings were correlated with corresponding histopathologic appearances. In two cases, the tumor cells were polygonal to spindle-shaped and were loosely arranged in a matrix of mucoid material. The histopathologic examination of the resected tumors in these cases revealed a classic pattern. In the third case, the aspiration smears revealed round to polygonal cells with moderate to abundant cytoplasm but without the mucoid matrix. The predominant histologic appearance of this tumor was an epithelioid trabecular pattern. Electron microscopic findings were similar to those described in published studies.

Electron microscopy of large cell undifferentiated and giant cell tumors

Electron microscopy is a valuable morphologic method for the diagnostic evaluation of undifferentiated tumors composed of polygonal or oval large cells and mononuclear or multinucleated giant cells. Although few ultrastructural details are pathognomonic, electron microscopic findings may add significantly to the formulation of the final diagnosis if used in the context of other pathomorphologic and clinical data. Contributions of electron microscopy to tumor diagnosis are summarized and illustrated with appropriate examples from personal experience in a routine university hospital laboratory.

Rhabdomyosarcoma of the maxillary sinus: review of the literature and report of a case

A case of rhabdomyosarcoma of the maxillary sinus is reported. A brief review of the origin, histomorphology, classification, clinical presentation, behavior, prognosis, and treatment is given relative to occurrence in the maxillary antrum. Misinterpretation of the microscopic findings can delay the histologic diagnosis. An error in tissue diagnosis may be minimized by awareness of a chance encounter with this lesion.

The intraclonal and interclonal phenotypic heterogeneity in a rhabdomyosarcoma cell line with abortive imitation of embryonic myogenesis

Three distinct subpopulations (A, B, C) derived from a dimethylbenzanthracene-induced rat rhabdomyosarcoma were established as permanent cell lines. Although the clonal nature of each of these subpopulations was confirmed by repeated recloning procedures, a striking intraclonal phenotypic heterogeneity was observed. By means of immunofluorescence microscopy and transmission electron microscopy, it could be shown that these subpopulations closely recapitulate stages of embryonic rhabdomyogenesis both in vitro and in vivo, but differ in their particular range of maximum differentiation. Embryonic rhabdomyogenesis is imitated most perfectly by subpopulation C, in which multinuclear myotubes are formed in vitro by fusion of mononuclear cells, and alpha-sarcomeric actin is expressed in the multinuclear cells and in a few mononuclear cells. After retransplantation in vivo, subpopulation C further proceeds in fine structural differentiation, now exhibiting myofibrils with a sarcomeric organization in the myotube-like giant cells. The cells of subpopulation B do not exceed the stage of mononuclear desmin-positive cells in vitro, but synthesize thin and thick myofilaments after retransplantation in vivo. The cells of subpopulation A recapitulate embryonic rhabdomyogenesis least successfully being confined to the stage of mononuclear desmin-positive cells. Thus, the coexistence of diverse subpopulations and the cellular maturation within these subpopulations together contribute to the phenotypic heterogeneity of rhabdomyosarcomas.

Primary rhabdomyosarcoma of the kidney. A light microscopic, immunohistochemical, and electron microscopic study

Primary rhabdomyosarcoma of the kidney is a rare and highly aggressive tumor in the adult population. A case is reported in a 70-year-old woman with the diagnosis confirmed by immunohistochemistry and electron microscopy. This is the first case studied using the immunoperoxidase technique and the second with electron microscopic examination. To make a diagnosis of primary sarcoma, of the kidney, three criteria must be met: (1) a metastatic sarcoma must be ruled out; (2) the tumor must arise from renal parenchyma; and (3) a sarcomatoid variant of renal cell carcinoma needs to be excluded. The literature is reviewed and available clinical and pathologic details are summarized.

Embryonal rhabdomyosarcoma

Rhabdomyosarcoma is one of the most common malignancies of the mesenchymal tissue in the head and neck region. A case of a 26-year-old male with oral rhabdomyosarcoma is presented. The clinical and pathologic aspects of this malignancy are also reviewed. Furthermore, the histopathologic and ultrastructural features of this neoplasia are described and the important role of electron microscopy in diagnosis of the myogenic tumor is emphasized. Finally, different modes of treatment for the rhabdomyosarcoma are discussed.

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.

Malignant triton tumour in the cerebellopontine angle. Report of a case

A report is given of a 24-year-old woman with a malignant cerebellopontine angle tumour, which appeared to have arisen from the 8th nerve sheath. It had a predominantly fasciculated, spindle-cell, Schwannoma-like structure, but also included rhabdomyoblastic elements and a diagnosis of malignant triton tumour is proposed. The patient did not have Von Recklinghausen's disease.

Synovial sarcoma: ultrastructural and immunohistochemical features of epithelial differentiation in monophasic and biphasic tumors

Nineteen synovial sarcomas, six biphasic and 13 monophasic tumors, were examined by light and electron microscopy and immunohistochemically for the presence of the epithelial markers keratin and epithelial membrane antigen (EMA). Ultrastructurally, intercellular spaces with processes are present to varying degrees in the spindle cell component of all synovial sarcomas, and junctional specializations occur in most cases. Tumors of the two types differ in their content of external (basal) lamina, which encloses the epithelial component of all biphasic tumors and is detectable in the spindle cell component of two thirds of them, but is absent from the majority of monophasic tumors. Keratin and EMA were demonstrated in both components of all six biphasic tumors. Of the 13 monophasic tumors, keratin was present in nine, EMA in eight, and at least one epithelial marker in ten. Synovial sarcoma is regarded as a distinctive soft tissue tumor with variable epithelial-like differentiation. The use of electron microscopy can increase the specificity of immunohistochemical studies of soft tissue sarcomas and allow more accurate differentiation of monophasic synovial sarcoma from other spindle cell tumors, particularly those that do not express markers.

Extraosseous Ewing's sarcoma versus primitive rhabdomyosarcoma: diagnostic criteria and clinical correlation

A light and electron microscopic study of 51 cases of Ewing's sarcoma of bone (ESB) and 33 soft tissue sarcomas (carrying a variety of light microscopic diagnoses, including primitive rhabdomyosarcoma) in children and young adults was performed to clarify the similarities and differences among these tumors. Ultrastructural criteria were developed to evaluate the neoplasms. Remarkable ultrastructural uniformity was found in the cases of ESB. In contrast, the soft tissue sarcomas could be divided into two distinct groups on the basis of the ultrastructural criteria: those closely resembling primitive areas of otherwise differentiated rhabdomyosarcomas, and those indistinguishable from ESB. It is proposed that the diagnosis of soft tissue Ewing's sarcoma be reserved for lesions identical to ESB by both light and electron microscopy. The first group of sarcomas may be histogenetically related to rhabdomyosarcoma and should be distinguished from extraosseous Ewing's sarcoma, as their clinical behavior appears to be quite different.

Tumors of skeletal muscle

The most common tumors arising in muscle are soft tissue sarcomas, fibromatoses, and hemangiomas. Rhabdomyosarcoma is primarily a tumor of childhood and adolescence and arises most commonly in extramuscular sites. Most intramuscular rhabdomyosarcomas are alveolar. Increased diagnostic accuracy and the recognition of malignant fibrous histiocytoma have changed understanding of adult, intramuscular, pleomorphic rhabdomyosarcoma. Immunohistochemistry is playing an increasingly important role in the diagnosis of rhabdomyosarcoma, and the correlation between the histologic features and clinical behavior of rhabdomyosarcoma is under investigation. Because of their diversity and overlapping histologic features, muscle tumors are a challenge for the pathologist and require intensive study by current techniques.

Fine-needle aspiration biopsy diagnosis of round cell malignant tumors of childhood. A combined light and electron microscopic approach

A series of fine-needle aspiration biopsies (FNAB) from 76 children with round cell malignant tumors was studied by both light and electron microscopy. In 14 cases the material submitted for electron microscopy was inadequate, whereas in the remaining 62 biopsies a definitive diagnosis could be made. These included 29 malignant lymphomas, 8 neuroblastomas, 12 Ewing's sarcomas, 3 metastatic retinoblastomas, 3 Wilms' tumors, 3 rhabdomyosarcomas, and 4 unclassified tumors. The results from this study indicate that FNAB studied by light and electron microscopy can be effective in diagnosing small cell tumors in children.

Small cell tumours in childhood: a review

The past decade has seen significant advances in the treatment of childhood malignancies accompanied by appreciable improvement in survival rates. Treatment programmes have been largely formulated to meet the specific characteristics of individual tumours, as well as being based on the extent of disease presented at diagnosis. In selecting the most appropriate treatment protocol, accurate histological categorization of resected or biopsied tumour is thus of paramount importance. In the paediatric age range in which so many tumours lack differentiation as to present as, or mimic, other small cell tumours, routine methods are often insufficient to resolve problematic histology. A wide range of special techniques is now at hand to assist the pathologist with this problem and this review is an attempt partly to rationalize the application of available methodology. Of considerable importance also is a knowledge of the behavioural characteristics of this group of tumours, their prototypic histology, as well as the range of morphological variability.

Ultrastructural distinctions between adult pleomorphic rhabdomyosarcomas, pleomorphic liposarcomas, and pleomorphic malignant fibrous histiocytomas

The ultrastructural features of five pleomorphic rhabdomyosarcomas, five high-grade malignant fibrous histiocytomas, and five pleomorphic liposarcomas were studied. Electron microscopy was found to be consistently useful in distinguishing between these tumors. The rhabdomyosarcomas showed thick and thin filaments in complexes and consistently contained glycogen. The malignant fibrous histiocytomas had numerous lysosomes, often in cells with ruffled borders, and contained cells showing "myofibroblastic" differentiation. The liposarcomas showed abundant and coalescing lipid droplets, sparse stroma with condensation of amorphous granular materials surrounding plasma membranes, and prominent vascularity. Fourteen of the 15 tumors could be identified on the basis of ultrastructure; thus, electron microscopic examination is an important diagnostic tool for pleomorphic tumors.

An investigation of beta enolase as a histological marker of rhabdomyosarcoma

Sections from 21 tumours diagnosed as primary or metastatic rhabdomyosarcoma were stained for alpha and beta enolase. The cases were subdivided into embryonal and alveolar subtypes (38% and 62%, respectively). Positive cytoplasmic staining for alpha enolase was seen in all but one case, and cytoplasmic staining for beta enolase was seen in some cells in 18 of the 21 cases (86% of the total, 88% of the alveolar subgroup, and 85% of the embryonal subgroup). No cells stained positively for beta enolase in the control series of neuroblastomas, fibrosarcomas, Wilms' sarcomas, and an osteosarcoma. The results show that beta enolase is a sensitive marker of muscular differentiation in rhabdomyosarcoma.

Medullomyoblastoma. A histologic, immunohistochemical, and ultrastructural study

The light and electron microscopic features of a medullomyoblastoma arising in the cerebellar vermis of a 3-year-old boy are described. Differentiation along both glial and neuronal lines was present in the medulloblastoma component of the tumor. Astrocytic differentiation was confirmed by the observation of compact bundles of 8 to 10 nm glial filaments in cellular processes on ultrastructural examination, and by positive immunostaining for glial fibrillary acidic protein (GFAP). Neuroblastic differentiation was suggested by the demonstration of axon-like processes on silver impregnation, and ultrastructurally by the observation of microtubules, dense-core and clear vesicles, and rare synapse-like structures within cytoplasmic processes. The presence of both primitive and well-differentiated striated muscle fibers in the tumor was confirmed by the demonstration of thick and thin myofilaments and Z bands on electron microscopy, and by positive immunostaining for myoglobin. These findings clearly establish the presence of both neuroectodermal and rhabdomyoblastic components in this neoplasm, and thus set it apart from the pure rhabdomyosarcomas, which may also occur in the cerebellar vermis in children. This case also illustrates the usefulness of electron microscopy and immunohistochemistry in the diagnosis and histogenetic evaluation of primitive or poorly differentiated small cell tumors of the central nervous system.

Pulmonary rhabdomyosarcoma with isolated small bowel metastasis. A report of a case with immunohistochemical and ultrastructural studies

A unique case of pulmonary rhabdomyosarcoma with an isolated, symptomatic small bowel metastasis is presented. The tumor affected the middle lobe, and was treated with a right pneumonectomy. Eleven months after the operation, an isolated small bowel metastasis, which produced intestinal obstruction, was resected. The patient is currently alive, 11 months after operation. The myogenous nature of the tumor was confirmed by the immunohistochemical demonstration of myoglobin in the pulmonary and enteric lesion by the ultrastructural findings of poorly developed sarcomeres.

Diagnosis and behavior of juvenile rhabdomyosarcoma

The main problems in the diagnosis of rhabdomyosarcoma are 1) distinction of undifferentiated examples from other small cell malignancies, especially soft-tissue Ewing's tumor and lymphoma; 2) distinction of spindling examples from fibrosarcoma, leiomyosarcoma, malignant fibrous histiocytoma, polyhistioma, and other sarcomas; 3) recognition of minimal criteria on small samples such as needle biopsy specimens or frozen sections; and 4) recognition of rhabdomyosarcoma in uncommon sites such as bone (mandible), perineum, retroperitoneum, and chest. In 95 pediatric cases diagnosed and treated at Royal Alexandria Hospital for Children--45 after the introduction of combined therapy--minimal diagnostic criteria were assessed. Cross-striations were found in only one third of cases; longitudinal myofibrils were more common and more helpful. There was much overlap between histologic types, and the microscopic patterns had little bearing on prognoses in preadolescent children. Fourteen cases could not be further differentiated ("embryonal sarcoma, probably rhabdomyosarcoma")--nine small-cell tumors; four tumors from genitourinary tract or head for which very small biopsy specimens were available, and one spindling retroperitoneal neoplasm. In all, slight evidence suggested embryonal rhabdomyosarcoma; this evidence included oat-shaped nuclei and, in a few cells, deeply eosinophilic cytoplasm, small elongated processes, or myxoid or alveolar foci--features that exclude lymphoma and Ewing's tumor. In six cases that were originally classified as poorly differentiated or undifferentiated, later material confirmed the presence of rhabdomyosarcoma by showing a predominantly well-differentiated (pleomorphic) or alveolar pattern after therapy. In 14 remaining undifferentiated cases, immunoperoxidase staining with antihuman-myoglobin serum was positive in five. With combined therapy there was 100 per cent survival among patients with paratesticular, limb, and stage I and stage II tumors; considerably improved survival among patients with head and neck, pelvic, and stage III tumors; and 100 per cent mortality among patients with intra-abdominal and stage IV tumors.