Microtubular aggregates within rough endoplasmic reticulum: an unusual ultrastructural feature of extraskeletal myxoid chondrosarcoma

Extraskeletal myxoid chondrosarcoma: updated clinicopathological and molecular genetic characteristics

Extraskeletal myxoid chondrosarcoma (EMC) is a rare soft-tissue sarcoma characterized by distinctive morphological and cytogenetical features. As its name implies, EMC was believed to represent a variant of soft-tissue chondrosarcoma owing to its histological resemblance to chondroblastic tissue in the early stages of cartilage development or chondroid tumors such as skeletal chondrosarcoma. However, the chondroid nature has been a subject of controversy, and its line of differentiation remains to be determined. Consequently, the tumor is provisionally classified into a group of tumors of uncertain differentiation in the revised World Health Organization classification of tumors of soft tissue and bone. Moreover, immunohistochemical and ultrastructural features of neural or neuroendocrine differentiation have been recently reported in a subset of EMC, providing a new insight into their histogenetic nature. Chromosomal rearrangements involving 9q22, such as t(9;22)(q22;q12), and resultant NR4A3 fusion genes are tumor-type specific or pathognomotic for this entity and are assumed to play an important role in the development of EMC. Although the biological mechanisms and functions are largely unknown, the NR4A3-related pathway is considered a potential molecular target for future therapeutic intervention. Because of its protracted but resilient nature, a tenacious and long-term follow up is necessary for any patient.

Coexpression of NOR1 and SIX3 proteins in extraskeletal myxoid chondrosarcomas without detectable NR4A3 fusion genes

Extraskeletal myxoid chondrosarcoma (EMC) is a rare mesenchymal tumor cytogenetically characterized by reciprocal translocations, such as t(9;22)(q22;q12) and t(9;17)(q22;q11), which result in EWSR1/NR4A3 and TAF15/NR4A3 fusion genes (alias EWS/NOR1, TAF2N/NOR1), respectively. NOR1 is an orphan nuclear receptor and acts as a transcription factor that can bind to its putative coactivator, SIX3. Although the NOR1 fusion protein has been implicated in oncogenesis of EMC, a small fraction of EMC lacks detectable rearrangements of the NR4A3 gene or 9q22. We report a case of EMC with no detectable NR4A3 gene alterations, as assessed with various molecular techniques including reverse transcription-polymerase chain reaction (RT-PCR), Southern blotting, interphase fluorescence in situ hybridization, and PCR single-strand conformation polymorphism-but with coexpression of native NOR1 and SIX3. In our survey of another 18 EMCs, we identified one more case expressing both NOR1 and SIX3 but lacking NR4A3 fusion. Fourteen tumors with detectable NR4A3 fusion genes (EWSR1-NR4A3; TAF15-NR4A3) expressed neither native NOR1 nor SIX3. SIX3 expression is normally confined specifically to the developing eye and fetal forebrain, although the expression of NR4A3 is largely ubiquitous. Our data suggest that aberrant coexpression of NOR1 and SIX3 is a potential alternative mechanism underlying the development of EMC.

Microtubule-associated protein-2 and class III beta-tubulin are expressed in extraskeletal myxoid chondrosarcoma

Extraskeletal myxoid chondrosarcoma is a rare soft tissue sarcoma of uncertain histogenetic origin. Because recent reports have indicated neural-neuroendocrine differentiation in some extraskeletal myxoid chondrosarcomas, we investigated 25 tumors for expressions of microtubule-associated protein-2 and Class III beta-tubulin, which are major components of microtubules and specifically localized in neurons and their derivatives. Immunohistochemical expression of microtubule-associated protein-2 and Class III beta-tubulin was studied in extraskeletal myxoid chondrosarcomas using formalin-fixed, paraffin-embedded tissues. Cytoplasmic expressions of microtubule-associated protein-2 and Class III beta-tubulin were detected in 21 (84%) and 13 (52%) of the 25 extraskeletal myxoid chondrosarcomas, respectively, although the number of positively stained tumor cells varied. Expression of the Class III beta-tubulin gene was also assessed in two immunohistochemically positive cases by in situ hybridization using an oligonucleotide probe specific for its transcript, and both cases showed expression of Class III beta-tubulin transcript. Another case was examined with immunoelectron microscopy, and immunogold particles for Class III beta-tubulin were localized to microtubular aggregates. Our data indicate that microtubules in extraskeletal myxoid chondrosarcoma are similar to those found in neurons, further supporting the concept that neural-neuroendocrine differentiation occurs in a significant number of extraskeletal myxoid chondrosarcoma.

Omental malignant fibrous histiocytoma with a unique rough endoplasmic reticulum inclusion

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

Extraskeletal myxoid chondrosarcoma: a light microscopic, immunohistochemical, ultrastructural and immuno-ultrastructural study indicating neuroendocrine differentiation

AIMS

Extraskeletal myxoid chondrosarcoma is a rare low-grade soft-tissue sarcoma with locally aggressive and metastasizing potential. Extraskeletal myxoid chondrosarcoma has distinctive clinical, light microscopic, immunophenotypic, cytogenetic and ultrastructural features. Evidence that extraskeletal myxoid chondrosarcoma often shows neuroendocrine features was first provided by Chhieng et al. on the basis of an immunohistochemical and ultrastructural study of seven cases. Our study aims to further confirm by immunohistochemistry and ultrastructural studies, including immunoelectron microscopy, that extraskeletal myxoid chondrosarcoma indeed may show neuroendocrine differentiation.

METHODS AND RESULTS

Fifteen cases of extraskeletal myxoid chondrosarcoma and seven control cases of skeletal chondrosarcomas were studied. Extensive immunohistochemical analysis was performed in all cases and ultrastructural studies were done in 11 extraskeletal myxoid chondrosarcomas and three skeletal chondrosarcomas. Immunoelectron microscopy was performed on one case each of extraskeletal myxoid chondrosarcoma and skeletal chondrosarcoma. Extraskeletal myxoid chondrosarcomas expressed neuron-specific enolase (100%), synaptophysin (87%), S100 (50%), PGP 9.5 (40%), and epithelial membrane antigen (25%). Co-expression of synaptophysin and PGP 9.5 was observed in six tumours. Skeletal chondrosarcomas showed expression of S100 protein, vimentin and neuron-specific enolase in all cases. Synaptophysin, chromogranin and PGP 9.5 were not expressed in any skeletal chondrosarcoma case. Ultrastructurally, extraskeletal myxoid chondrosarcoma was characterized by distinct cords of cells immersed in a glycosaminoglycan-rich matrix. The cells were rich in mitochondria, had well-developed Golgi apparatus and there were numerous smooth vesicles. In three cases there were easily found 140-180 nm diameter membrane-bound dense-core granules in cell bodies and in processes, unrelated to the Golgi, compatible with neurosecretory granules. Fewer such granules were present in the remaining extraskeletal myxoid chondrosarcoma cases, three of which also contained intracisternal tubules typical of extraskeletal myxoid chondrosarcoma. The skeletal chondrosarcomas had scalloped cell surfaces, prominent rough endoplasmic reticulum focally distended with secretory product, and lacked neurosecretory granules. Intermediate filaments were prominent in both extraskeletal myxoid chondrosarcoma and skeletal chondrosarcomas. Immunoelectron microscopy showed synaptophysin expression in the extraskeletal myxoid chondrosarcoma but not in the skeletal chondrosarcoma case.

CONCLUSIONS

This study confirms that a substantial proportion of extraskeletal myxoid chondrosarcomas show immunophenotypic and/or ultrastructural evidence of neuroendocrine differentiation, and are unlikely to be related to conventional skeletal chondrosarcomas.

Extraskeletal myxoid chondrosarcoma: a clinicopathologic, immunohistochemical, and molecular analysis of 18 cases

Extraskeletal myxoid chondrosarcoma (EMCS) is an uncommon clinicopathologically well-defined tumor, but its pathogenesis and biologic behavior are poorly understood. We reviewed 18 cases of EMCS to verify clinicopathologic features and immunohistochemical profiles together with molecular detection of the tumor-specific fusion genes. The tumors were located mainly in the proximal extremities and limb girdles (72%). Two tumors arose at unusual anatomic sites: the finger and the hip joint. Nine of the 17 followed-up patients were alive and disease free, 4 were alive with recurrences and/or metastases, and 4 died of the tumor. Fifteen tumors showed typical features of EMCS, and 3 had hypercellular areas in addition to conventional EMCS areas. The tumors were variably immunoreactive for S-100 protein (50%), NSE (89%), peripherin (60%), and synaptophysin (22%). Chromogranin A and some epithelial markers (AE1/AE3, CAM5.2, and epithelial membrane antigen) were entirely negative. Frequent expressions of the neural/neuroendocrine markers suggest possible neural/neuroendocrine differentiation in at least some EMCSs, in addition to chondroid differentiation. In a reverse-transcription polymerase chain reaction (RT-PCR) assay using paraffin-embedded specimens, EWS-CHN or TAF2N-CHN fusion gene transcripts characteristic of EMCS could be detected in 15 (83%) of the 18 cases: EWS-CHN type 1 in 11 cases, EWS-CHN type 2 in 1, and TAF2N-CHN in 3. Three fusion-negative cases included 2 conventional EMCSs and 1 considered a "cellular" variant of the tumor. None of 30 other soft tissue and bone tumors with myxoid or chondroid morphology that we examined contained these fusion genes. Thus, RT-PCR detection of EWS-CHN or TAF2N-CHN fusion gene using archival paraffin-embedded tissue is a feasible and useful ancillary technique for the diagnosis of EMCS.

Extraskeletal myxoid chondrosarcoma: a clinicopathologic, immunohistochemical, and ploidy analysis of 23 cases

Twenty-three cases of extraskeletal myxoid chondrosarcoma, evaluated at the Mayo Clinic between 1968 and 1996, were studied for clinicopathologic features, immunohistochemical profile, Ki-67 activity, and ploidy status to identify adverse prognostic factors. Females and males were equally affected, and the median age at diagnosis was 50 years. The tumors were located mainly in the lower extremities (83%), and the median tumor size was 9.5 cm. Sixteen tumors showed low cellularity (70%), and eight tumors had high mitotic activity (more than two per 10 high-power fields). The tumors were immunoreactive for vimentin (89%), synaptophysin (72%), epithelial membrane antigen (28%), and S-100 protein (17%). Nine tumors were diploid, three aneuploid, and one tetraploid. Mean Ki-67 activity was 11% (range, 1 to 45%). The 10-year overall survival rate was 78%. On univariate analysis, tumor size > or = 10 cm, high cellularity, presence of anaplasia or rhabdoid features, mitotic activity more than two per 10 high-power fields, Ki-67 > or = 10%, and Ki-67 "hot spot" > or = 25% were associated with decreased metastasis-free or overall survival. Ploidy status was not associated with any adverse outcome. The presence of any of these adverse prognostic factors can indicate the possibility of a more aggressive behavior in extraskeletal myxoid chondrosarcoma, and a closer follow-up is suggested.

Malignant myxoid endobronchial tumour: a report of two cases with a unique histological pattern

AIMS

To present two cases of malignant endobronchial myxoid tumours with a highly distinctive sarcomatoid pattern not previously described at this site, and discuss their histogenesis in relation to previously documented endobronchial neoplasms.

METHODS AND RESULTS

Both tumours presented in young adult females and were purely sarcomatoid with interweaving cords of small uniform, rounded or slightly elongated cells lying within a myxoid stroma. The stroma was alcian blue positive, but sensitive to hyaluronidase in both cases. The tumour cells contained a small volume of periodic acid-Schiff-positive eosinophilic cytoplasm and stained positively for vimentin only, but there also was a prominent background population of CD68-positive dendritic cells. Ultrastructural studies showed that the tumour cells contained an excess of rough endoplasmic reticulum, with some of the cisternae appearing dilated, and scalloping of the cell surfaces, although no intracisternal tubules were identified.

CONCLUSIONS

Although the histological pattern was most reminiscent of extraskeletal myxoid chondrosarcoma, the sensitivity of the stroma to pretreatment with hyaluronidase precluded the diagnosis. However, there were similarities with the sarcomatoid component of malignant salivary gland-type mixed tumours of the lung and this tumour possibly represents a variant of a bronchial gland tumour. Despite this uncertainty over origin, this pattern should be recognized as part of the differential diagnosis of myxoid tumours in the lung, as an apparently indolent type of malignant endobronchial neoplasm.

High-grade extraskeletal myxoid chondrosarcoma: a high-grade epithelioid malignancy

AIMS

Extraskeletal myxoid chondrosarcoma is typically a low-to-intermediate grade sarcoma that is associated with a prolonged clinical course. High-grade forms are rare and not well characterized. In this series we report the clinicopathological, immunohistochemical and ultrastructural findings in four cases of high-grade extraskeletal myxoid chondrosarcoma.

METHODS AND RESULTS

The patients were three men and one woman (ages 34-73 years) with tumours located in the thigh (two cases), paraspinal soft tissue and perineum. Three patients had metastases, one at 12 weeks, one at 10 months, and one at presentation of recurrent tumour. In the latter case the original tumour was low grade and became high grade when it recurred 3.5 years later. All three patients died of disease. One patient was lost to follow-up. The most striking histological feature in all four tumours was the presence of numerous large epithelioid cells. These cells were arranged in cords within myxoid matrix and in sheets devoid of matrix. Two tumours had areas of conventional extraskeletal myxoid chondrosarcoma intermixed with the high-grade areas. One tumour showed transition to high-grade spindle cell sarcoma. One tumour had cells with rhabdoid features. Immunohistochemically, two tumours focally expressed S100 protein, and one focally expressed EMA. All were negative with cytokeratin, desmin, smooth muscle actin, HMB45, CD31 and CD34. Ultrastructural features in three cases were compatible with chondrosarcoma; one tumour had aggregates of microtubules within rough endoplasmic reticulum, a characteristic feature of this tumour.

CONCLUSIONS

High-grade extraskeletal myxoid chondrosaroma is a rare and aggressive soft tissue sarcoma, and should be included in the differential diagnosis of other epithelioid malignancies.

Microtubular aggregates within the rough endoplasmic reticulum of embryonal rhabdomyosarcoma cells: a case report

This study presents a case of embryonal rhabdomyosarcoma (ERMS) of the forearm soft tissue in a 12-year-old female, in which microtubular aggregates in rough endoplasmic reticulum (rER) were noted ultrastructurally. Histologically, tumor cells consisted of typical rhabdomyoblastoid cells with abundant eosinophilic cytoplasm and relatively immature, small tumor cells. Ultrastructurally, two different types of tumor cells were also identified by light microscopy. More than half the tumor cells possessed the characteristic features of rhabdomyoblastic differentiation, such as abundant thick and thin filaments with Z-bands. The other tumor cells were less differentiated cells in which microtubular aggregates (MA) in rER were observed. MA in rER have been described in several nonepithelial tumors, including malignant melanoma, osteosarcoma, extraskeletal myxoid chondrosarcoma, and chordoma. ERMS is another example of mesenchymal tumor in which MA in rER are observed by electron microscopy. Considering the differential diagnosis among mesenchymal tumors, it is important to know that MA can be also observed in ERMS.

Skeletal and extraskeletal myxoid chondrosarcoma: a comparative clinicopathologic, ultrastructural, and molecular study

BACKGROUND

Skeletal myxoid chondrosarcoma (SMC) is considered to be either a typical chondrosarcoma with prominent myxoid alterations or an altogether unique malignant cartilage tumor. Extraskeletal myxoid chondrosarcoma (EMC) is a relatively rare but well-recognized neoplasm. It was initially thought to be a low grade sarcoma of cartilage derivation and was recently found, in most cases, to contain a reciprocal t(9;22), resulting in a fusion of the EWS and CHN genes. Are SMC and EMC the same entity arising in two different locations, or are they two separate entities? To the authors' knowledge, this study represents the first systematic attempt to answer this question.

METHODS

Forty consecutive cases of EMC (20 cases) and SMC (20 cases) were compared by light and electron microscopy, immunohistochemistry, and molecular analysis. The mean clinical follow-up for both groups was 55 months. Histologic criteria for SMC consisted of 95% myxoid matrix, with only minimal hyaline cartilage formation.

RESULTS

The gender distribution was identical in both groups (13 males and 7 females). The mean age was 55 years for EMC patients and 45 years for SMC patients. The EMC tumors were predominantly located in the deep soft tissues of the lower extremity (60%) and buttock (20%), and the mean tumor size was 13 cm. SMC was most commonly located in the bones around the hip joint (pelvis 35%; proximal femur 20%) and shoulder (20%); the mean size was 9 cm. Histologic grade in the EMC group correlated with survival (82% of the high grade tumors metastasized). Electron microscopy performed in 8 EMC cases revealed intracisternal microtubules in 3 cases and prominent mitochondria in 5, whereas in 5 SMC cases it revealed only inconspicuous organelles. Molecular analysis for the EWS-CHN fusion RNA resulting from the t(9;22) was performed in 15 cases (9 EMC and 6 SMC) and was detected in 7 of 9 EMC cases and 0 of 6 SMC cases. In one case, the molecular structure of the EWS-CHN fusion RNA was novel. The probability of metastasis was significantly higher (P=0.004) for the EMC group than for the SMC group.

CONCLUSIONS

Although similar light microscopic features are noted in EMC and SMC, fundamental differences are noted at the ultrastructural and molecular levels, suggesting that EMC and SMC represent two distinct entities in the chondrosarcoma family of tumors.

Parachordoma: a clinicopathologic and immunohistochemical study of four cases of an unusual soft tissue neoplasm

Four soft tissue tumors corresponding with the previously reported parachordoma are described. Three of the patients were men, and one was a woman, and their ages ranged from 14 to 53 years (mean age, 29). The tumors were located either superficially or within muscle, and, in one case, involved a tendon. Histologically, the tumors displayed whorls, nests, and pseudoglandular cords of uniform polygonal cells with eosinophilic, vacuolated cytoplasm, in a focally myxoid stroma. Transitions were seen between fascicles of ovoid-spindled cells, with scanty cytoplasm in a fibrous stroma, and, in one case, whorls of bland spindly cells were also present. Electron microscopy of one case showed cells with short interdigitating microvilli and ill-defined junctions. The principal cells in all cases were positive for S100 protein, Leu-7, keratin (CAM5.2), and epithelial membrane antigen (EMA). All tumors were negative with antibody AE1 and with antibodies to cytokeratins CK7 and CK19. No tumor displayed immunoreactivity for carcinoembryonic antigen (CEA), muscle specific actin (MSA), smooth muscle actin (SMA), desmin, glial fibrillary acid protein (GFAP), CD31, or CD34. Parachordoma appears to be an entity with clinical and pathological differences from chordoma, which has a different cytokeratin profile, behaves in a more aggressive fashion, and can dedifferentiate. The differential diagnosis includes myxoid chondrosarcoma, myoepithelial cell tumor, ossifying fibromyxoid tumor, and chondroid lipoma.

Myxoid chondrosarcoma of soft tissue and bone: a retrospective study of 11 cases

This article describes 11 cases of myxoid chondrosarcoma (MCS), with 10 arising in soft tissues and one developing in bone. Most of the tumors (six) were located in the lower extremities. Two lesions developed in the fingers, a previously unreported location for MCS. Four cases showed secondary bone destruction, which is a rare feature of this tumor. S100 protein was expressed by tumor cells in all the specimens. Four out of eight tumors studied by electron microscopy contained intracisternal microtubular structures. Two tumors showed areas of spindle cell proliferation that merged with the areas of typical myxoid pattern. The cells in these areas had fibroblastic/myofibroblastic features by electron microscopy and were found to express cytokeratin by immunohistochemistry. The concomitant expression of cytokeratin and S100 protein in the spindle cells suggests that they represent a less differentiated cartilaginous component with unusual features. The clinical significance of the presence of such spindle cell areas presently remains unknown. Although myxoid chondrosarcoma is a slow-growing tumor, it has a high potential for metastases. Four of 11 patients in this series developed metastases.

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.

FNA of extraskeletal myxoid chondrosarcoma: cytomorphologic, EM, and X-ray microanalysis features

Extraskeletal myxoid chondrosarcoma, an unusual soft tissue lesion which preferentially affects the extremities, is a prime candidate for "pathologist performed" fine-needle aspirates (FNA) because it preferentially affects the extremities [Enzinger and Shiraki, Hum Pathol 1972;3:421-435] and is usually an accessible lesion. Cytomorphologically, the neoplasm consists of clusters of fairly uniform cells, lacking cartilaginous differentiation, with a metachromatic matrix when stained with Diff-Quik (DQ). While subtle, this neoplasm has distinct features and must be distinguished for other neoplasms in the differential diagnosis because patient evaluation, prognosis, and therapy will vary greatly. We present a case characteristic of this tumor in which FNA derived material was subjected to light microscopy, X-ray microanalysis, and immunohistochemical studies; each modality provided data essential to the correct diagnosis.

Extraskeletal myxoid chondrosarcoma with intracisternal microtubules

A case of extraskeletal myxoid chondrosarcoma with intracisternal microtubules is presented. The microtubules were generally straight, parallel, closely packed, and evenly spaced, but they did not form geometric arrays. Aggregates of stromalike myxoid material were present in the cisternae and the adjacent cytoplasm. Microtubules were never found within the cytoplasm. A similar ultrastructural appearance was seen in 4 of 10 other examples of extraskeletal myxoid chondrosarcoma.

Intracranial extraskeletal myxoid chondrosarcoma with special reference to lamellar inclusions in the rough endoplasmic reticulum

An extraskeletal myxoid chondrosarcoma in the pineal region was studied by light and electron microscopy. The immunohistochemical positivity for S-100 protein, vimentin and collagen type II favored a chondrocytic origin of the tumor. In addition to the well-described ultrastructural features suggestive of a cartilagenous nature, this tumor had unusual lamellar inclusions in the rough endoplasmic reticulum. To the best of our knowledge, this is the first report of these special inclusion bodies in a myxoid chondrosarcoma.

Parachordoma: an ultrastructural and immunohistochemical study

A case of parachordoma of the left calf in a 19-year-old Chinese female is reported. The tumour showed multinodular growth pattern and consisted of round or oval tumour cells with abundant eosinophilic cytoplasm and myxoid matrix. Tumour cells formed small nests and sometimes showed concentric arrangement. Physaliferous-like cells and undifferentiated spindle cells were occasionally observed among the cell nests. The myxoid matrix was positive for high-iron diamine stain, indicating the presence of chondroitin 4- and 6-sulphates and keratan sulphate. Ultrastructurally, well-developed rough endoplasmic reticulum, abundant intermediate filaments, microvillous cytoplasmic processes, pinocytic vesicles, and desmosome-like junctional structures were found. Tumour cells were positive for S-100 protein and vimentin, but negative for cytokeratin, epithelial membrane antigen, carcinoembryonic antigen, and desmin. These results are consistent with the definition of parachordoma as a soft tissue neoplasm consisting of cells with histology and ultrastructure similar to those of chordoma cells but with immunohistochemistry similar to that of chondroid tumour cells.

Unusual extraskeletal myxoid chondrosarcoma

We describe an unusual soft tissue tumor occurring within the rectus femoris muscle of a 64-year-old woman. The site, size, macroscopic, and histological appearances were all consistent with an extraskeletal myxoid chondrosarcoma. However, the present case differs significantly from previous reports of this uncommon tumor in that electron microscopy did not show any evidence of chondroblastic differentiation. Furthermore, the cells failed to stain for vimentin while labeling intensely for neuron-specific enolase, contained large numbers of cytolysosomes having a multivesicular appearance, and focally produced an external lamina. Based on the typical histological appearances we conclude that this is an unusual variant of extraskeletal myxoid chondrosarcoma in which there is evidence of nerve sheath differentiation.

Chromosomal abnormality t(9;22)(q22;q12) in an extraskeletal myxoid chondrosarcoma characterized by fine needle aspiration cytology, electron microscopy, immunohistochemistry and DNA flow cytometry

A multidisciplinary approach was taken to characterize a soft tissue tumour. In smears prepared from aspirated material, uniform tumour cells, embedded in a myxoid matrix and partly arranged in a lace-like pattern, were found. Histopathology showed a lace-like pattern of cells in a matrix of hyaluronidase-stable mucins. Cytoplasmic positivity for S-100 protein was found in some tumour cells. Electron microscopic analysis revealed intracisternal aggregates of microtubules. All these features are consistent with the diagnosis of extraskeletal myxoid chondrosarcoma (EMC). DNA flow cytometry showed a diploid DNA content. Cytogenetic examination revealed the tumour karyotype 45,XY,t(2;11)(q31;p15),t(9;22)(q22.3;q12),dic(13;22)(p11;p13). Because similar 9;22-translocations have been described in two other cases of EMC, we conclude that t(9;22)(q22-31;q11-12) is a specific rearrangement in this tumour type. Cytogenetic analysis may thus be of diagnostic value in the examination of tumours with this and similar histologies.

Microtubular aggregates in the rough endoplasmic reticulum of sacrococcygeal chordoma

A tumor with the light microscopic and immunohistologic characteristics of chordoma in the sacrococcygeal region in a 48-year-old man was examined by electron microscopy and immunohistochemistry for tubulin. A large population of cells exhibited prominent parallel arrays of long, straight microtubules in the rough endoplasmic reticulum in addition to the well-described ultrastructural features of chordoma. Immunoreaction to tubulin recognized in the juxtanuclear regions of the large number of tumor cells was in accordance with the ultrastructural localization of the microtubular aggregates. This seems to be the first report of microtubular aggregations in rough endoplasmic reticulum in classic chordoma. Furthermore, the present electron microscopic and immunohistochemical findings suggest that tubulin is a constituent of the unusual structures.

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.

Extraskeletal myxoid chondrosarcoma characterized by microtubular aggregates in the rough endoplasmic reticulum and tubulin immunoreactivity

A case is reported of a 66-year-old female with an extraskeletal myxoid chondrosarcoma which had originated in the lateral region of the right knee. The tumour tissue of the primary, recurrent, and metastatic deposits in the lungs was examined by electron microscopy and immunohistochemistry. Almost all the sarcoma cells in every tumour specimen harboured immunoreactivity to both alpha- and beta-subunits of S-100 protein. A large population of cells in the subcutaneous tumour at autopsy had numerous parallel arrays of microtubules within the rough endoplasmic reticulum in addition to the well-described ultrastructural features indicative of chondroblastic origin. These structures were present in round to polygonal, but not in fibroblastic, tumour cells. Tubulin immunoreactivity in the tumour cells showed the same tendency, being frequently positive in the large cells of the subcutaneous tumour but weakly positive in the fibroblastic and medium-sized cells of the recurrent and metastatic tumours. The parallel arrays of intracisternal microtubules therefore may be composed of tubulin protein, as in ordinary cytoplasmic microtubules.

Straight intracisternal tubules in rough endoplasmic reticulum of human melanoma cells

This case presentation illustrates peculiar tubular aggregates in rough endoplasmic reticulum (RER) of human melanoma cells, a location in which they have been reported in a small percentage of malignant melanomas.