An EMA negative, desmin positive malignant mesothelioma: limitations of immunohistochemistry?

Histopathologists in the current environment of medical negligence and litigation are more likely to use immunohistochemical investigations in their day-to-day practice to support their diagnosis and avoid future litigation. The caveat is that relying on immunohistochemistry is a double-edged sword and pathologists should be familiar with its limitations. We present a case of primary malignant peritoneal mesothelioma with an unusual immunohistochemical profile-desmin positive, EMA negative-and wish to highlight the importance of cautiously interpreting immunohistochemistry profiles when they do not fit the clinical history and histological appearance.

The myofibroblast and its tumours.

Tumours and tumour-like lesions of myofibroblasts may present diagnostic difficulty because of their rarity and because of uncertainties in identifying the myofibroblast. The objectives of this review are to provide a definition of the myofibroblast and an account of its biology for facilitating an understanding of the cell and of myofibroblastic lesions; and to describe, in the context of common diagnostic problems, the features of benign and malignant myofibroblastic lesions. The main characteristics of the myofibroblast include a spindled or stellate morphology; immunostaining for alpha-smooth muscle actin and the extra domain A variant of cellular fibronectin; and an ultrastructure of rough endoplasmic reticulum, peripheral contractile filaments and the cell-to-matrix junction known as the fibronexus. On this basis, lesions traditionally regarded as myofibroblastic are shown to vary in their level of differentiation, and some appear to be smooth muscle rather than myofibroblastic. Immunohistochemistry and electron microscopy, used together, are emphasised as being important for maximum diagnostic confidence in some myofibroblastic lesions.

The myofibroblast: phenotypic characterization as a prerequisite to understanding its functions in translational medicine.

The phrase translational research' conveys the idea of the pursuit of applications for the treatment of human disease. The myofibroblast, long known for having a role in wound-healing, and for its presence in fibrotic conditions and tumour stroma, is becoming a focus for translational research, not least through its increasingly documented role as a tumour-promoting cell. In fibroproliferative conditions, cancer and tissue engineering, the myofibroblast, derived partly and possibly from circulating bone-marrow-derived cells and epithelial-to-mesenchymal transformation, is attracting great attention. In cancer, this cell was initially regarded as a barrier to tumour dissemination, but there is now a growing body of evidence to indicate that it is an active participant in tumour progression. While the involvement of the myofibroblast in these pathological processes is pushing the myofibroblast into the limelight of translational medicine as a target for potential anti-fibrotic and anti-cancer therapy, there are still numerous indications from the literature that the myofibroblast is a poorly understood cell in terms of its differentiation.Partly, this is due to a failure to appreciate the contribution of electron microscopy to understanding the nature of this cell. This paper, therefore, is devoted to detailing the principal phenotypic characteristics of the myofibroblast and promotes the argument that understanding how the myofibroblast carries out its roles in normal biological and in pathological processes will be enhanced by a sound understanding of its cellular differentiation, which in turn arguably demands a significant ultrastructural input.

Divergent differentiation in malignant melanomas: a review.

The aim of this review was to document and discuss diagnostic problems associated with divergent differentiation ('metaplastic change') in malignant melanomas, defined as the development in these tumours of morphologically, immunohistochemically and/or ultrastructurally recognizable non-melanocytic cell or tissue components. Types of divergent differentiation reported in malignant melanoma include: fibroblastic/myofibroblastic, Schwannian and perineurial, smooth muscle, rhabdomyosarcomatous, osteocartilaginous, ganglionic and ganglioneuroblastic, neuroendocrine and probable epithelial. Divergent differentiation is certainly a rare phenomenon and, when it occurs, can be missed by unwary pathologists and lead to diagnostic uncertainty. A carefully chosen immunohistochemical panel and the input of electron microscopy can help to clarify the nature of the cellular differentiation of these tumours and lead to a correct final diagnosis. The clinical significance of such aberrations is uncertain, nor are the underlying mechanisms as yet well defined.

The myofibroblast: a study of normal, reactive and neoplastic tissues, with an emphasis on ultrastructure. Part 1--normal and reactive cells.

The myofibroblast is essential for the integrity of the mammalian body by virtue of its role in wound-healing, but it can also threaten it by its ability to promote tumour progression. It is an almost universal cellular component in mammalian lesions, but not a typical component of normal untraumatised tissues. Partly because of its absence from normal tissue, it has not been part of conventional histology teaching. This has contributed to difficulties in appreciating the nature of the myofibroblast and defining it by scientists interested in the mechanism of disease and pathologists wanting to diagnose myofibroblastic rumours. This paper documents the features of the myofibroblast with an emphasis on ultrastructure. A base-line of understanding is first provided by a description of normal cells found in untraumatised tissues, from which the myofibroblast has on occasion been postulated as arising, or with which, to varying degrees, the myofibroblast has been confused--fibroblasts, smooth-muscle cells, endothelium, pericytes, myoepithelium and lymphoid reticulum cells. The biology, light microscopy features and ultrastructure of the myofibroblast are then documented for comparison. Features emphasised for defining the myofibroblast include: a spindled cell morphology, an abundant matrix, immunostaining for alpha-smooth-muscle actin (in the absence of desmin and h-caldesmon) and the ED-A splice variant of cellular fibronectin, rough endoplasmic reticulum, peripherally located smooth-muscle type myofilaments, a Golgi apparatus producing collagen-secretion granules, gap junctions and fibronexus junctions. The fibronexus is emphasised as a distinctive organelle for identifying the myofibroblast and lamina is emphasised as absent. The mechanism by which myofibroblasts arise in granulation tissue and promote tumour progression is discussed briefly, and an appendix provides summaries of the involvement of myofibroblasts in non-neoplastic diseases.

Primary smooth muscle tumor of the pleura: a clinicopathological case report with ultrastructural observations and a review of the literature.

Primary smooth muscle tumor of the pleura is exceptionally rare. The authors describe a primary smooth muscle tumor of the pleura that was discovered incidentally on chest X-ray in a 73-year-old man. Magnetic resonance imaging demonstrated a 12 x 18 x 15-cm pleura-based mass arising from the posterior mediastinum. Computerized tomography (CT) guided needle cores from the pleura showed a primary smooth muscle tumor of undetermined malignant potential. Further excision of the whole tumor showed an intimate relation to pleura, and the diagnosis of leiomyosarcoma was made. The clinical, radiological, histopathological, immunohistochemical, and ultrastuctural findings were consistent with a primary smooth muscle tumor of the pleura. This is the seventh case in the literature of a primary smooth muscle tumor of the pleura, which, to the best of the authors' knowledge, is the first such case of the pleura to be diagnosed on CT-guided needle biopsy. In conclusion, this method of investigation is recommended since it is minimally invasive but has a rewarding yield in providing the most likely diagnosis, predicting prognosis, and management planning.

Malignant melanoma with neuroendocrine differentiation: clinical, histological, immunohistochemical and ultrastructural features of three cases.

AIM: To document the clinical, histological, immunohistochemical and ultrastructural features of three malignant melanomas showing neuroendocrine differentiation. METHODS AND RESULTS: Three patients, two with primary cutaneous melanoma and one with nasal mucosal melanoma, subsequently developing or simultaneously presenting with metastatic malignant melanoma, were studied by conventional histological technique, immunohistochemistry of formalin-fixed paraffin-wax embedded tissues, and electron microscopy of epoxy-resin-embedded tumour tissue. Tumours showed either small cell or conventional malignant melanoma cell morphology. One of the three primary melanocytic lesions (the nasal melanoma) exhibited neuroendocrine differentiation immunohistochemically. All three metastatic malignant melanomas showed, in varying combinations, immunohistochemical and ultrastructural evidence for neuroendocrine differentiation: they were positive for the melanocytic markers, S100 protein, HMB-45, Melan-A and tyrosinase, and the neuroendocrine markers chromogranin, synaptophysin and neurofilament protein. Ultrastructural study in two of the metastases revealed neuroendocrine granules but no lattice-bearing melanosomes. CONCLUSIONS: The cases described are the most comprehensively investigated malignant melanomas showing neuroendocrine differentiation to date, and the first to document neuroendocrine differentiation ultrastructurally in these tumours. Malignant melanoma with neuroendocrine differentiation therefore needs to be recognized among the other, better known variants of malignant melanoma.

Foci of amorphous/granulofilamentous matrix in the extracellular domain of tumours. 2. Immunohistochemical and immunogold characterization of a fibronectin-rich matrix component.

The term FEAM (foci of extracellular amorphous matrix) has been used for discretely outlined areas of moderately dense material having a filamentous/granular substructure located in the extracellular matrix of tumours. In spite of being widespread in mesenchymal tumours especially, and often abundant, they have received little attention in terms of structure, composition and origin. Mostly, they have been regarded as a variant or a product of lamina ('basement membrane material'). However, they also appear in tumours whose cells should and do lack a lamina, such as giant-cell fibroblastoma and solitary fibrous tumour. This paper describes their fine structure in a variety of predominantly mesenchymal tumours, and documents their composition using light microscope immunostaining and immunogold labelling. Small amounts of type IV collagen and laminin were found focally and inconsistently among the five tumours by light microscope immunostaining, but fibronectin was strongly and consistently identified. Strong fibronectin staining was also identified by immuno-electronmicroscopy. These data suggest that FEAM represent a fibronectin-rich matrix constituent, which might be a common final product of either lamina or the external component of the subplasmalemmal linear density (focal adhesion). There is little support light microscopically for a relationship to immune-complexes or cryoglobulins.

The myofibroblast: a study of normal, reactive and neoplastic tissues, with an emphasis on ultrastructure. part 2 - tumours and tumour-like lesions.

This paper describes the ultrastructure of the commoner myofibroblastic tumours and tumour-like lesions. The objective is to complement mainstream pathology texts, which have concentrated on the clinical and light microscopy features of these lesions and which have arguably but understandably somewhat neglected electron microscopy as an ancillary diagnostic tool and a technique for investigating tumour cell biology. Ultrastructural features are described of nodular fasciitis, the myofibromatoses (including Dupuytren's disease), inflammatory myofibroblastic tumour, post-operative spindle cell nodule, fibroma of tendon sheath, fibrous pseudotumour, benign fibrous histiocytoma, atypical fibroxanthoma, dermatofibrosarcoma protuberans, myofibrosarcoma (myofibroblastic sarcoma), malignant fibrous histiocytoma (pleomorphic myofibrosarcoma), epithelioid sarcoma and spindle-cell carcinoma. Fibrosarcoma and leiomyosarcoma are illustrated for comparison. The fibronexus is emphasised as an important marker for the most confident diagnosis of myofibrosarcoma. Some pathologists accept a light microscope definition, which includes alpha-smooth-muscle actin positivity, h-caldesmon negativity and, in some cases, desmin positivity. Caution in the interpretation of desmin staining in a possible myofibroblastic lesion is urged, since, in combination with an ultrastructurally identified lamina, it more probably suggests true smooth-muscle differentiation. Myofibroblastoma and angiomyofibroblastoma are examples of tumours argued on the basis of ultrastructural findings (sometimes in combination with desmin staining) to be primitively differentiated smooth-muscle cell rather than myofibroblastic proliferations.

Actin filaments in human renal tubulo-interstitial fibrosis: significance for the concept of epithelial-myofibroblast transformation.

Epithelial-myofibroblast transformation has been argued as playing a role in tubulo-interstitial fibrosis. To investigate this hypothesis, we examined 9 renal biopsy specimens from patients with chronic renal disease by light and electron microscopy. In all cases, electron microscopy confirmed light microscope observations in relation to tubulo-interstitial fibrosis-tubular atrophy, accumulation of extracellular matrix and of mesenchymal interstitial cells, and infiltration by inflammatory cells. Tubular epithelial cells (TECs) contained bundles of actin filaments: mostly lacking the focal densities typical of smooth-muscle myofilaments. The interstitium contained collagen and inflammatory cells. Some endothelial cells showed bundles of myofilaments. Free mesenchymal cells in the matrix were spindled and had sparse rough endoplasmic reticulum (rER), small attachment plaques, few actin filaments and no lamina. In one case, myofibroblasts (defined by abundant rER, myofilaments and fibronexuses) were present. Most of the mesenchymal cells, therefore, did not correspond to myofibroblasts, nor to classical fibroblasts because of the sparse rER and the presence of actin filaments. We therefore called these cells myoid stromal cells, regarding them as stromal mesenchymal elements showing partial activation towards a smooth-muscle phenotype. This paper demonstrates a greater phenotypic complexity of actin-containing stromal cells in the interstitium than previously appreciated, with only a minority conforming to true or fully differentiated myofibroblasts. The widespread presence of actin (as filaments or immunoreactivity) in both TECs and interstitial cells, combined with the absence of evidence of intermediate forms or of migration from epithelium into interstitium, may point to epithelium and interstitium as separate targets for actin upregulation as an alternative hypothesis to epithelial-myofibroblast transformation.

Foci of amorphous/granulofilamentous matrix in the extracellular domain of tumours: a study of 34 cases. 1. Ultrastructural characterisation.

The distribution and the appearance of foci of extracellular amorphous/granulofilamentous material (FEAM) in 34 human tumours are described. FEAM were rounded to oval, or more elongated or irregular elements of discretely delineated dense material lying in the extracellular space of tumours. They varied in size and abundance, sometimes coalescing into more extensive areas of dense material. At high magnification, FEAM exhibited a granular and finely filamentous substructure. Variations in the electron-density of FEAM were noted. Some FEAM were found associated with the surfaces of tumour cells, on occasion with subplasmalemmal linear densities. FEAM was also sometimes associated with matrix filaments, often collagen. Material of similar substructure and density was also associated with some vessels. FEAM were mostly found in tumours showing mesenchymal differentiation. The nature and origin of FEAM is discussed.

The ultrastructure of human tubulo-interstitial fibrosis.

Tubulo-interstitial fibrosis, comprising tubular atrophy, infiltration by inflammatory cells, accumulation of extracellular matrix, and proliferation of mesenchymal cells in the interstitium, is a major characteristic of most progressive chronic renal diseases leading to end-stage renal failure, regardless of cause. All of the ultrastructural characteristics of tubulo-interstitial fibrosis can correlate with clinically defined features of chronic renal dysfunction. The present review illustrates ultrastructural features, emphasising some novel findings, in tubulo-interstitial fibrosis, including widespread expression of actin filaments, fatty degeneration of tubular epithelial cells, presence of cilia, and infiltration of leukocytes into the tubular lumen. The hypothesised development of interstitial myofibroblasts from tubular epithelial cells, and the relationship between tubule injury and capillary abnormality are also discussed.

Cardiac sarcoma showing bone formation and neurogenic markers: report of a case.

A 54 year-old Japanese female with cardiac insufficiency was found to have a left atrial mass and smaller masses on the mitral valve. Excisional surgery of the masses and mitral valve replacement were carried out. In spite of intensive post-operative radiation therapy, the patient died of intra-atrial recurrence and brain metastases after 8 months. Tumour cells were spindled to oval, were positive for vimentin, S100 protein and neurone specific enolase. Laminin and fibronectin were also demonstrated. Bone formation and myxoid areas were present. An ultrastructurally identifiable stromal component, possibly responsible for laminin and fibronectin staining, was also present. The merits of the two main diagnostic possibilities - a mesenchymal/fibroblastic sarcoma showing bone and aberrant S100 protein, and a malignant peripheral nerve sheath tumour with bone - were discussed. In practical terms, the tumour was given the diagnosis of unclassifiable sarcoma of the left atrium. Atrial sarcomas showing neural markers and bone formation are exceedingly rare, and this report adds a further exceptionally uncommon case to the literature.

Amphicrine carcinoma of breast with giant granules: an immunohistochemical, histochemical and ultrastructural study.

A moderately differentiated grade 2 invasive ductal carcinoma was diagnosed in the right breast of an 81-year-old woman. The uniform nuclear profiles and moderately abundant granular cytoplasm suggested a neuroendocrine tumour and a Grimelius stain was positive. Neurone specific enolase, synaptophysin and somatostatin stained positively, and casein was interpreted as positive although with some background staining. By electron microscopy, tumour cells possessed desmosomes, tonofibrils, intercellular lumina, lamina and dense granules. Rounded dense granules 160-480 nm in diameter resembled neuroendocrine granules. They were found in both luminal and basal areas. Fewer and much larger ('giant') granules had a rounded profile and were up to 5 microm across. The smaller cytoplasmic granules were mostly Grimelius-positive while giant granules were negative. The smaller granules were also uranaffin-positive, but no uranaffin-positive cytoplasmic giant granules were encountered. Both small and giant granules were observed in lumina, and here both were uranaffin-positive. Intraluminal giant granules had a substructure of small pale lipid-like lacunae, and some had irregular profiles. The exceptional size of these exocrine granules is emphasised, and the nature of both the small and giant granules discussed in this amphicrine carcinoma.