Micronodular PEComas of the appendix.

AIMS: Perivascular epithelioid cell tumours (PEComas) of the appendix have been reported very rarely. In this study, we describe three cases of a distinctive micronodular proliferation in the appendix consistent with a variant of PEComa. Although known as 'granular degeneration of smooth muscle' in prior reports, we reappraise its clinicopathological, immunohistochemical and ultrastructural features which support a change in classification. METHODS AND RESULTS: Patients were two females (aged 33 and 41 years) and one male (aged 41). None had a history of tuberous sclerosis. Histologically, each case demonstrated a multifocal nodular proliferation towards the distal tip of the appendix, composed of epithelioid cells with abundant granular eosinophilic to clear cytoplasm. By immunohistochemistry, the lesional cells were positive for muscle markers [smooth muscle actin (SMA) and desmin], melanocytic markers (HMB45, melan A), cathepsin K and the lysosomal marker NKI-C3 in each case. MITF was positive in two of three cases. None expressed S100 protein. Electron microscopy in one case revealed striated electron-dense structures consistent with pre-melanosomes. Follow-up, available in one case, showed no recurrence at 5 years. CONCLUSIONS: We propose the term 'micronodular PEComa' for this appendiceal lesion to reflect more accurately its histological and immunohistochemical characteristics, which include consistent positivity for both muscle and melanocytic markers. Micronodular PEComa seems to follow an indolent course, consistent with its uniformly low-grade histological features, and appears to be unassociated with tuberous sclerosis.

Signet ring cell angiosarcoma: a hitherto unreported pitfall in the diagnosis of epithelioid cutaneous malignancies.

We report 2 cases of cutaneous epithelioid angiosarcoma featuring predominantly signet ring cells. The patients-a woman, 68 years of age, and a man, 85 years of age, respectively-were referred for slowly growing indurated plaques on their parietal and retroauricular skin. Microscopic examination showed diffuse dermal proliferations comprising polygonal cells and relatively abundant cytoplasm. Because the tumor cells often were distended by variably sized vacuoles pushing the nuclei to the periphery, the nuclear profile tended toward a crescent-like morphology. Abortive luminal formations were recognized. The tumor cells were positive for CD31, CD34, and D2-40/podoplanin, with no expression of epithelial or melanocytic markers. In 1 case, upon ultrastructural examination of paraffin-embedded tissue-cut from wax tissue and reprocessed-the optically empty spaces were surrounded by a membrane with ultrastructural features identical to those of the outer cell membrane, suggesting that these spaces corresponded to the formation of primitive intracytoplasmic lumina within the tumor cells. A few Weibel-Palade bodies also were noted. Our report offers further evidence that epithelioid angiosarcoma of the skin has a broad microscopic spectrum and that tumors displaying a preponderant population of signet ring cells pose further diagnostic challenges. A brief overview of cutaneous malignant tumors in the differential diagnosis of signet ring cell angiosarcoma is provided.

Deciduoid mesothelioma: report of 21 cases with review of the literature.

Deciduoid mesothelioma is a rare variant of epithelioid mesothelioma that was initially considered to occur exclusively in the peritoneum of young women who had no history of asbestos exposure and to be characterized by an aggressive clinical course, but it was later demonstrated that this tumor could also occur in the pleura of older men and women who had been exposed to asbestos. Some subsequent studies have also indicated that the clinical course is no different from that of conventional epithelioid mesothelioma. Herein are reported 21 cases of deciduoid mesothelioma that were investigated using a large panel of immunohistochemical markers, 9 of which were also studied by electron microscopy. Fifteen of the patients were male and 6 were female (mean age, 60 years). Seventeen of the cases originated in the pleura and four in the peritoneum. Histologically, all of the cases were composed of large, polygonal or ovoid cells with well-defined cell borders, dense eosinophilic cytoplasm, and single or multiple nuclei. In some cases, the cells exhibited a wide variation in their size and shape, frequent loss of cell cohesion, marked nuclear atypia, and high mitotic activity (>5 per 10 HPF); whereas, in others, the cells were more cohesive, less pleomorphic, and the mitotic activity low. As the survival of patients in the first group of cases was shorter (mean, 7 months), when compared with that of the latter (mean, 23 months), it is concluded that the differences in prognosis reported in deciduoid mesothelioma are due to the existence of a high-grade subgroup that presents highly aggressive clinical behavior. Therefore, when a high-grade deciduoid mesothelioma is present, it should be reported as it can significantly affect prognosis and treatment. The use of immunohistochemistry and electron microscopy in assisting in the differential diagnosis of deciduoid mesothelioma is also discussed.

A group of sclerosing epithelioid fibrosarcomas with low-level amplified EWSR1-CREB3L1 fusion gene in children.

Sclerosing epithelioid fibrosarcoma (SEF), typically arising in middle-aged and older adults, is a rare malignant fibroblastic neoplasm characterized by epithelioid fibroblasts embedded in sclerotic hyalinized stroma. This tumor frequently harbors translocation between EWSR1 and CREB3 subfamily members. Here, we describe four cases of SEF with unique genetic characteristics in children. All tumors were located in the deep soft tissue of the trunk and celom. Histopathologically, the tumors were featured by prominent hyalinized sclerotic collagenous stroma within which relatively bland and monomorphic epithelioid cells were arranged in cords, nests, or sheets. Low-grade fibromyxoid sarcoma-like zones varied among cases. MUC4 was strong and diffuse. CD99 was positive. Transmission electron microscopy demonstrated spindle or polyhedral neoplastic cells with a collagen fiber-rich stroma. Interphase fluorescence in situ hybridization (FISH) revealed local amplification of the EWSR1 locus. Whole-genome sequencing indicated translocation between EWSR1 and CREB3L1 together with low-level amplification of the fusion parts. RT-PCR and Sanger sequencing confirmed the fusion transcript. Single nucleotide polymorphism and FISH analyses demonstrated co-deletion of 11p and 22q. The consistent genetic features indicated the presence of a unique molecular variant of SEF. DATA AVAILABILITY STATEMENT: The data used to support the findings of this study are available from the corresponding author upon request.

Perivascular epithelioid cell tumor (PEComa) of the pancreas: immunoelectron microscopy and review of the literature.

A perivascular epithelioid tumor (PEComa) is a rare tumor probably arising from the perivascular epithelioid cells. Only three cases of pancreatic PEComa have been reported in the English-language literature. The present report describes an extremely rare case of pancreatic PEComa. A 47-year-old Japanese woman complained of lower abdominal pain and a well-demarcated solid tumor was found in the pancreatic head. There was no history of tuberous sclerosis complexes. Pylorus-preserving pancreaticoduodenectomy was thus performed. There was a well-demarcated, solid tumor measuring 17 mm in the pancreatic head. The tumor was composed of a diffuse proliferation of epithelioid tumor cells with many blood vessels but no adipose tissue. The tumor cells expressed HMB45 and alpha-smooth muscle actin. Ultrastructurally, the tumor cells possessed many membrane-bound granules that were positive for HMB45 on immunoelectron microscopy. The results of immunoelectron microscopy show that some PEComas possess not only typical melanosomes or premelanosomes but also aberrant melanosomes.

[Sclerosing epithelial fibrosarcoma: a clinico-morphological evaluation of 10 cases].

Sclerosing epithelial fibrosarcoma is a malignant mesenchymal tumor (fibroblastic class). It involved tissues of the legs and trunk in patients aged 31-59 and grew slowly as an infiltrative neoplasm during 6-18 months. Relapse occurred in 20% although no metastases were reported. Tumor consisted of epithelial fibroblasts with light cytoplasm and mononuclei. The latter showed low mitotic activity. Fibroblasts came in clusters, bands and alveolar formations sitting in the fibrous stroma. There were small areas consisting of bundles of spindle-shaped fibroblasts with oval hyperchromatic nuclei. Differentiated analysis of epithelioid fibrosarcoma may also be done by computed microscopy and immunomorphology using other tumor models consisting of light-cytoplasm epitheloid cells, mostly osteosarcoma, clear-cell renal carcinoma, melanoma, synovial sarcoma and clear-cell sarcoma of the tendon sheath and aponeurosis.

Perivascular epithelioid cell neoplasms (PEComas): four malignant cases expanding the histopathological spectrum and a description of a unique finding.

Four cases of malignant PEComas were stained with smooth muscle actin, muscle specific actin, desmin, human melanoma black-45, melan-A, microphthalmia transcription factor, S100 and cyclin D1. One case was studied by electron microscopy (EM). Tumour locations were the thigh, elbow, retroperitoneum and bladder in association with a urachal cyst. There were two men and two women; the average age was 51.3 years, and the size ranged from 5.0-23.0 cm. In three cases, 50-95% of the tumour was composed of pleomorphic sarcomatous areas. All cases had at least focal clear-cell areas. One case showed a continuous single layer of perivascular clear cells remote from the tumour, transitioning to invasive nests and to PEComa. EM demonstrated these cells in apposition to and in direct contact with the abluminal surface of the basal lamina of the capillaries. We suggest the term "pecosis" for these areas. All cases were positive for two or more melanocytic markers and for at least one actin. S100 and desmin were focally positive in one case. Cyclin D1 was positive in 3:4 cases. Four cases of malignant PEComa are described with the existence of a unique lesion (pecosis) in one case. These tumours may manifest largely as sarcomas appearing to be undifferentiated and should be considered in their differential diagnosis.

[PEComa of soft tissue: report of an articular case]. / PECome des tissus mous: à propos d'un cas de localisation articulaire.

We report a case of PEComa (or perivascular epithelioid cell tumor) in an unusual articular localization in a 13-year-old boy. The tumor, of 4 cm in diameter, showed an infiltrative pattern and was composed of both epithelioid and spindle cells with clear to granular eosinophilic cytoplasm and some multinucleated giant cells. Focal nuclear pleomorphism was present and we found up to 2 mitotic figures /50 high power field. There was no necrosis. Immunohistochemistry showed HMB-45 and smooth muscle actin positivity. Ultrastructurally, premelanosomes were present. Some rare cases of PEComa were reported in the soft tissues. The immunohistological profile (HMB-45 and smooth muscle actin positivity and PS-100 negativity) is helpful to the diagnosis. The histological prognostic criteria of these tumors are not well established. We discuss here the differential diagnosis, notably clear cell sarcoma of soft tissue.

[Epithelioid angiomyolipoma of kidney: clinicopathologic study of two cases and review of literature].

OBJECTIVE: To study the histopathologic features, differential diagnosis and prognosis of epithelioid angiomyolipoma (EAML) of kidney. METHODS: Two cases of EAML (including one case with recurrence) of kidney were retrieved from the archival files of Departments of Pathology, Navy General Hospital of PLA and Health Science Center of Peking University. The clinicopathologic features, immunohistochemistry, ultrastructural findings and follow-up data were studied and literature reviewed. RESULTS: Histologically, the tumors were predominantly composed of epithelioid cells with marked cellular pleomorphism. Focal perivascular arrangement was seen. Hemorrhage and necrosis were present and tumor emboli were found in the venous structures. The renal hilar lymph nodes were also involved by tumor cells. Immunohistochemical study showed that the tumor cells (including those in the hilar lymph nodes) were strongly and diffusely positive for HMB45, smooth muscle actin, neuron-specific enolase and vimentin. They were focally positive for S-100 protein, melan-pan and CD68. The staining for epithelial membrane antigen, AE1/3, CK7, CD117, muscle-specific actin, desmin, leukocyte common antigen, CD20, CD45RO, CD30, CD15, chromogranin A, synaptophysin, bcl-2, estrogen receptor, progesterone receptor and p53 were negative. Ultrastructural examination revealed the presence of melanosome-like dense granules, myofilaments and dense bodies in the tumor cell cytoplasm. Discontinuous and focally thickened basal lamina was seen surrounding the tumor cells. On follow up, both patients remained well and disease-free 10 months after operation. CONCLUSIONS: EAML is predominantly or almost entirely composed of epithelioid cells. Perivascular cellular arrangement, focal features of otherwise classic angiomyolipoma, as well as coexpression of HMB-45 and smooth muscle actin are clues to the correct diagnosis. The degree of cytologic atypia, presence of hemorrhage and necrosis and high mitotic activity may indicate the malignant potential of this tumor. On the other hand, the presence of lymph node involvement and even tumor emboli in renal veins may represent multifocaltumorigenicity rather than true malignancy. Definitive evidence of malignancy requires demonstration of distant metastasis.

Clear cell myomelanocytic tumor of the falciform ligament/ligamentum teres: a novel member of the perivascular epithelioid clear cell family of tumors with a predilection for children and young adults.

The perivascular epithelioid cell family of tumors (PEComas), defined by their co-expression of melanocytic and muscle markers, includes angiomyolipoma, lymphangioleiomyoma, and clear cell "sugar" tumors of the lung, pancreas, and uterus. We present seven cases of a unique and previously unrecognized tumor of children and young adults, which represents a new addition to the PEComa group of tumors. Culled from three institutions over a 50-year period, all cases occurred in or immediately adjacent to the ligamentum teres and falciform ligament. Six patients were female and one male; their ages ranged from 3 to 21 years (median, 11 yrs). Tumor sizes ranged from 5 to 20 cm (median, 8 cm). All cases consisted of clear to faintly eosinophilic spindled cells arranged in fascicular and nested patterns. The cells had small but distinct nucleoli and low mitotic activity. Immunohistochemically, all cases were positive with antibodies to gp100 protein (HMB-45) and negative for S-100 protein. In three of the seven cases studied immunohistochemically, the tumors expressed smooth muscle actin, melan-A, microphthalmia transcription factor (MiTF), and myosin, but not desmin. No expression of the TSC2 gene product, tuberin, was seen in three cases. One case studied cytogenetically disclosed a t(3;10). Follow-up data, available in six of seven cases (median duration, 18 mos), showed five patients to be free of disease and one to have a radiographically presumed lung metastasis. We think these tumors comprise a new entity for which we propose the term "clear cell myomelanocytic tumor of the falciform ligament/ligamentum teres." The differential diagnosis of these tumors includes clear cell sarcoma of tendons and aponeuroses, leiomyosarcoma, and angiomyolipoma.

Epithelial-mesenchymal transition in proliferative vitreoretinopathy: intermediate filament protein expression in retinal pigment epithelial cells.

PURPOSE: To improve our understanding of how retinal pigment epithelial (RPE) cells behave in vivo and to establish similarities with dedifferentiation and adaptive events observed in RPE cells cultured under simulated intraocular pathologic conditions. At the same time, to examine the origin of epithelioid-shaped and fibroblast/fusiform-shaped cells in epiretinal membranes (ERM) from proliferative vitreoretinopathy (PVR). METHODS: Cells of ERM were studied by electron-immunocytochemical techniques, using simple, double, and triple immunostaining for cytokeratins (CK), vimentin (Vim), and glial fibrillary acidic protein (GFAP). Ultrastructural morphology analysis was also carried out. Adult human RPE cells were obtained and cultured with normal and pathologic vitreous from proliferative vitreoretinal disorders, subretinal fluid aspirates from retinal detachment, and normal human serum. Their cytoskeleton was fractionated at 7 (early cultures) and 24 (late cultures) days of culture, electrophoresed, immunoblotted for intermediate filament proteins, and quantified by densitometric analysis for each condition. Changes in phenotype characteristics were also evaluated. RESULTS: Epithelioid-shaped and fibroblast/fusiform-shaped cells, resembling RPE cells, expressed CK-Vim-GFAP simultaneously as intermediate filament proteins in their cytoskeleton. RPE cells in culture also expressed CK-Vim-GFAP and changed from an epithelial shape to a migratory fibroblast/fusiform-shaped phenotype in the presence of subretinal fluid aspirates and pathologic vitreous from proliferative intraocular disorders. In simulated cultures of proliferative intraocular disorders, cells decreased or retained their CK7, CK8, and CK18, retained Vim, and increased CK19 and GFAP, while their mesenchymal morphology became clearer over time. CONCLUSIONS: Studies of intermediate filament proteins in vivo suggest that dedifferentiation occurs in RPE cells in ERM. Dedifferentiated RPE cells may be responsible for epithelioid-like and fibroblast/fusiform-like cells. Furthermore, changes in intermediate filament protein levels were observed in RPE cells in simulated cultures of proliferative intraocular disorders. These changes were linked to cells acquiring a mesenchymal migratory, phenotype. Results indicate that the dedifferentiation of RPE cells occurs both in vivo and in vitro and that it can be explained as an epithelial-mesenchymal transition.

Ultrastructural heterogeneity of epithelioid cells in cutaneous organized granulomas of diverse etiology.

In organized granulomatous inflammation, activated macrophages terminally differentiate into epithelioid cells (ECs). By light microscopy, individual ECs appear similar, irrespective of the inciting agent. Ultrastructural analysis of a number of clinical and experimental granulomas in man and mice reveals, however, three distinct varieties of these cells. They are classified as follows: (1) EC-I cells containing a mixture of lysosomal-dense bodies and phagolysosomes and arrays of rough endoplasmic reticulum in the cytoplasm; (2) EC-II cells showing primarily a secretory mode with prominent Golgi bodies and rich arrangement of dilated rough endoplasmic reticulum with no phagocytic vacuoles; and (3) EC-III cells containing large multisized vesicles crowded throughout the cytoplasm and presently of unknown function. Although the unique appearance of these cells offers little diagnostic help, the cells do distribute differentially in different granulomas. The EC-I cells tend to predominate in infectious granulomas and where an excess of foreign material and debris is present. The EC-II cells are most characteristic of active sarcoidal granulomas, and the EC-III cells appear in chronic, long-standing granulomas. The heterogeneic nature of these cells seems to suggest their functions in granulomatous inflammation are not always the same.

Epithelioid ependymoma: a new variant of ependymoma: report of three cases.

OBJECTIVE: To describe the pathological features of three very similar and unusual primary central nervous system tumors that are not readily recognized as conventional ependymomas but which, by ultrastructural examination, have an ependymomatous character. METHODS: Three distinctive tumors were found in a review of our files for cases of ependymoma. In each case, hematoxylin and eosin-stained sections were reviewed, and immunostains for epithelial membrane antigen, cytokeratin, vimentin, and glial fibrillary acidic protein were performed on formalin-fixed, paraffin-embedded sections. Electron microscopy was performed in each case. RESULTS: The tumors had a diffuse myxoid background, often containing tightly clustered cells that mimicked multinucleated giant cells, but lacking perivascular pseudorosettes or central lumen rosettes. Glial fibrillary acidic protein and vimentin immunostains did not reveal perivascular processes. Epithelial membrane antigen immunostains showed a dot-like cytoplasmic immunoreactivity in some cell clusters in two of the three cases. Cytokeratin was negative in all three cases. However, ultrastructurally, the cells of each tumor had extensive surface microvilli; the giant cell-like clusters had cells with extensive close appositions, some junctions, and, in two cases, lumina with microvilli. Two of the patients were adults (both with temporal lobe tumors), and one patient was 13 years old and had a cervical spinal cord intramedullary tumor. Each tumor was sharply circumscribed from adjacent central nervous system tissue but was not encapsulated. One of the cases in an adult was mitotically highly active; this tumor recurred locally 4 years after initial gross total excision. CONCLUSION: These tumors are unusual variants of ependymoma. This pattern of ependymoma is sufficiently distinctive to be recognized in hematoxylin and eosin stains once the architecture of the epithelioid clusters is appreciated.

Murine macrophages cultured with IL-4 acquire a phenotype similar to that of epithelioid cells from granulomatous inflammation.

Epithelioid cells (ECs) found in granulomas are thought to derive from mononuclear phagocytes. Although GM-CSF and/or IL-4 are known to promote cell differentiation their role in the development of ECs has never been demonstrated. Here we showed that mouse macrophages treated exclusively with recombinant IL-4 (rIL-4) differentiate into epithelioid-like cells. Macrophages cultivated with rIL-4 presented a fried-egg shape, and ultrastructural studies revealed membrane interdigitations, cytoplasmic vesicles, prominent Golgi complex, and rough endoplasmic reticulum. Compared with controls, rIL-4 treated cells displayed increased expression of MHC class II molecules and of Migration Inhibitory Factor-Related Protein-14. Whereas mannose receptor-mediated phagocytosis was increased, Fcgamma-receptor mediated phagocytosis and the production of nitric oxide were decreased in treated cultures. All these features overlap those reported for ECs from granulomatous lesions. In conclusion, treatment of mouse peritoneal macrophages with rIL-4 drives their in vitro differentiation to an epithelioid phenotype and provides a tool to investigate the biology of ECs.

Macrophage and epithelioid cell nuclear morphology in leprosy.

The spectrum of disease in leprosy is characterised by the presence of macrophages in lepromatous lesions and epithelioid cells in tuberculoid granulomas. Since changes in nuclear shape occur during macrophage activation, we have measured nuclear morphology by planimetry in biopsies across the leprosy spectrum. The results show no significant correlation of any of the parameters of nuclear morphology measured between different lesions or between biopsies from the centre and edge of the same lesion. There were no differences between the Ridley-Jopling groups. However, several parameters which measure the degree of ellipticity of the nuclei showed strong correlation with granuloma size in untreated leprosy patients. This suggests that local pressure effects may influence epithelioid cell and macrophage nuclear morphology in leprosy lesions.

Perivascular epithelioid cell tumor of the jejunum.

Certain HMB-45-positive epithelioid cell tumors have recently been categorized under a unified concept: perivascular epithelioid cell tumor (PEComa). In this report, we describe ajejunal PEComa arising in a 32-year-old woman without other tumors or stigmata of tuberous sclerosis. The tumor consisted of nests of epithelioid cells with clear to granular eosinophilic cytoplasm. The nests were separated by thin fibrovascular septa. The tumor cells were positive for HMB-45 and progesterone receptor, and negative for cytokeratin, epithelial membrane antigen, vimentin, desmin, alpha-smooth muscle actin and CD34. RT-PCR analysis failed to reveal fusion transcript ETW/ATF1, which is characteristic of clear cell sarcoma of the soft parts. She developed a recurrent tumor at the pelvic wall and the left ovary at 13 and 25 months after the first operation, respectively. Each tumor was resected surgically, and no additional therapy was performed. We think the tumor of this case is a malignant form of PEComa because of the clinical history of multiple recurrences and the size of the primary tumor. Our case underscores that to make a correct diagnosis, clinical information and immunohistochemical examination are essential.

The current role of electron microscopy in the diagnosis of epithelial and epithelioid tumors.

Electron microscopy may be applied to the study of epithelial or epithelial-like tumors with benefits similar to those encountered when it is applied to other diseases. Thus, it may complement and allow us to understand the light microscopic appearance of tumors, help in tailoring or reducing the number of antibodies, or lead to diagnosis in cases with paradoxical or nonspecific immunocytochemical results. An important, newly suggested application is to use it as a quality assurance tool in the evaluation of cases already diagnosed by other methods. Tumors with epithelial phenotype are highly prevalent, and therefore the number of problem cases can also be relatively high. In this article, we review the main ultrastructural features used in the differential diagnosis of epithelial and epithelioid tumors and some potential pitfalls. In addition, we summarize the criteria for differential diagnosis in specific topographical areas and analyze some examples of how electron microscopy may improve the accuracy of pathological diagnosis by interacting with currently available immunocytochemical panels.

Malignant monotypic epithelioid angiomyolipoma of the retroperitoneum.

Monotypic epithelioid angiomyolipoma (EAML) is an uncommon variant of angiomyolipoma, occurring primarily in the kidney and characterized by a predominance of HMB-45-positive epithelioid cells. EAML is generally considered a benign neoplasm, though rare cases exhibiting malignant behavior have been reported. We describe a patient with a primary retroperitoneal monotypic EAML, composed exclusively of atypical epithelioid cells, which metastasized to the liver and the mediastinum. This case represents, to our knowledge, the first description of metastatic disease occurring in an EAML of this particular site.

Monotypic angiomyolipoma of the nasal cavity: a heretofore undescribed occurrence.

A monotypic angiomyolipoma of the nasal cavity in a 34-year-old woman is described. Tumor cells were spindled or epithelioid and contained glycogen and diastase-resistant PAS-positive granules. There were few mitoses, and necrosis was absent, indicating a benign tumor. The stroma was markedly vascular, and a few adipocytes were seen in one area. Cells were positive for melanocyte and muscle markers. Electron microscopy revealed abundant dense granules. Although melanin was absent histochemically, it was present using a chemical assay, and the granules may, therefore, be atypical melanosomes. Fine actin filaments, attachment plaques and lamina were present. Initial assessment of the lesion indicated malignant melanoma, but the immunostaining and histologic features indicated monotypic angiomyolipoma. To the best of our knowledge, this is the first such case in the nasal cavity.