Collagen secretion granules in reactive stromal myofibroblasts, with preliminary observations on their occurrence in spindle cell tumours

Dermatofibroma and Dermatofibrosarcoma Protuberans: A Comparative Ultrastructural Study

Dermatofibroma (DF) and dermatofibrosarcoma protuberans (DFSP) are dermal tumors whose histogenesis has not been well defined to date. The differential diagnosis in most cases is established in routine H/E sections and may be confirmed by immunohistochemistry, but there are atypical variants of DF with less clear histological differences and non-conclusive immunohistochemical results. In those cases, electron microscopy studies may be useful in establishing the diagnosis. The authors describe in detail the ultrastructural characteristics of 38 cases of DFSP and 10 cases of DF. The objective was to establish the ultrastructural features for differential diagnosis, and to identify the possible histogenesis of both neoplasms. DFSP is formed by stellate or spindled cells with long, slender, ramified cell processes joined by primitive junctions. Subplasmalemmal densities were frequently seen in the processes. Another common finding was the presence of multivesicular buds (MVB), peculiar structures that contain microvesicles abutting from the cell membrane. In contrast, DF is characterized by a proliferation of multiple capillary vessels with prominent endothelium and a perivascular population of ovoid or spindled cells devoid of cell processes. These latter cells featured intracytoplasmic lipid material (p < .001), infrequent subplasmalemmal densities (p < .001), and absence of MVB (p < .001). With the ultrastructural characteristics and the constant expression of CD34 in DFSP, a probable origin in dermal dendrocytes is postulated for this tumor. The histogenesis of DF is less clear, but an origin from FXIIIa modified perivascular dermal dendrocytes is proposed.

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.

Intracellular formation of collagen microfibrils in granulation tissue

It is important to determine the biosynthesis process of collagen fibers to elucidate the mechanism by which granulation tissue is induced after injury. The purpose of this study is to investigate whether collagen microfibrils can be formed not only outside but also inside a cell. Fibroblast-like cells in granulation tissue resulting from incision and ligation were examined. The cells possessed vesicles containing collagen microfibrils. The vesicles were present in connection with Golgi apparatus or the rough endoplasmic reticulum. Furthermore, the vesicles were exhibited to be secretory granules with the secretory granule marker Rab3A. The fibroblast-like cells were also indicated to be myofibroblasts, using conventional transmission electron microscopy and immunoelectron microscopy for the myofibroblast marker alpha smooth muscle actin. In conclusion, it was demonstrated that collagen microfibrils could be formed in the cell in the case of collagen fiber overproduction.

Fibroblast phenotype plasticity: relevance for understanding heterogeneity in "fibroblastic" tumors

Cellular transformations, reflecting phenotypic plasticity, characterize embryonic life, would-repair, physiological adaptation, and neoplasia. Fibroblastic tumors show a range of cellular differentiation, which can be rationalized in terms of phenotypic plasticity of the "normal" fibroblast. In this paper, the various kinds of fibroblast transformation are discussed, and some insights provided into the molecular mechanisms involved. Comparable molecular events may take place in neoplastic fibroblasts to produce the heterogeneous tumors nevertheless identified as fibroblastic. The following transformations are discussed: histiocytic, and fibrohistiocytic tumors; adipocytic, and lipogenic tumors; myofibroblastic, and myofibroblastic tumors. A definition of the fibroblast is required. This consists of spindle-cell morphology, vimentin-staining, and abundant rough endoplasmic reticulum. Transformation to histiocytic, lipogenic and myofibroblastic phenotypes requires the development of lysosomes, lipid droplets and lamina, and peripheral myofilaments and fibronexuses respectively. These occur in non-malignant transforming (transdifferentiating) fibroblasts, and also in tumors identified as fibrohistiocytic, lipogenic and myofibroblastic. The molecular basis of the myofibroblast transformation is probably the best studied. It is driven primarily by transforming growth factor beta. Investigations into the mechanisms of differentiation in normal fibrobiasts could prove fertile ground for defining comparable differentiation in tumors. In this respect, there are very few publications on the presence of growth factors in tumors or tumor-like lesions. There is, however, increasing investigation into gene expression and gene products in tumors, which bear on the differentiation process. Ultimately, our understanding of the molecular events controlling differentiation in cancer will lead to control, cure and prevention.

Myofibroblastic tumours: neoplasias with divergent behaviour. Ultrastructural and flow cytometric analysis

Myofibroblasts are spindle cells having ultrastructural features in common with smooth muscle cells and fibroblasts. In the last few years, tumours have been described in which myofibroblasts represent not only a reactive mechanism but also a true neoplastic component. They constitute new nosologic entities which might be termed "myofibroblastic tumours". Tumours with benign and, rarely, malignant behaviour are reported to belong to this group of lesions. Recently, a third tumour type with borderline biological course, named "inflammatory myofibroblastic tumour" (IMT), has been identified, a condition that has been regarded as a benign and reactive disorder for a long time. Only in recent reports has been demonstrated that, in spite of an apparently benign morphological pattern, some cases of IMT have a malignant course. In this connection, DNA analysis by flow cytometry is a valuable diagnostic tool, because it allows identification of the ploidy status, a procedure that is often useful for predicting the nature and the biological behaviour of the lesion. In this study, 11 cases of myofibroblastic tumours were examined retrospectively by evaluating clinicopathological features and DNA ploidy status by flow cytometry. The diagnosis of myofibroblastic tumour was confirmed by performing histology, immunohistochemistry, and electron microscopy in all patients. In detail, these 11 cases were composed of 1 benign myofibroblastoma, 1 myofibrosarcoma and 9 IMTs. Among these myofibroblastic tumours, all those with local recurrence or distant metastases (one myofibrosarcoma and three IMT) showed an aneuploid cell population demonstrable by flow cytometric analysis, whereas the other cases with benign course (one benign myofibroblastoma and six IMT) exhibited an euploid DNA content. These data suggest the following: a) Besides the rare myofibroblastomas and myofibrosarcomas, IMTs represent a larger group of lesions with potentially different biological and clinical course. b) DNA flow cytometric analysis is a reliable tool that support histopathological examination in characterizing those cases of IMT that, though being malignant, mimic benign lesions. Consequently, it establishes the basis for a different therapeutic approach according to the euploid or aneuploid DNA content.

Sclerosing epithelioid fibrosarcoma: a study of five cases emphasizing diagnostic criteria

AIMS

To study the clinical and histopathological features of sclerosing epithelioid fibrosarcoma, and to define diagnostic criteria for this uncommon soft-tissue tumour.

METHODS AND RESULTS

Standard histological, immunohistochemical and ultrastructural techniques were applied to five tumours from head and neck, chest wall and groin. Tumours consisted of groups of monomorphic rounded/epithelioid cells surrounded by a prominent collagenous stroma. Tumour cells showed positive vimentin staining but were negative for other markers. They contained prominent rough endoplasmic reticulum and a large Golgi apparatus which in one case was producing collagen secretion granules, an ultrastructural marker for collagen production. Three patients had medium to long-term survival (3-7 years). Of these, one was disease-free for 3 years, and two experienced multiple recurrences: one of the latter died of metastatic disease.

CONCLUSION

Criteria for diagnosing this uncommon tumour include: small to medium cell size, clear or pale cytoplasm, cellular arrangement in cords and strands, dense collagenous stroma; vimentin staining; rough endoplasmic reticulum and a Golgi apparatus producing, in well preserved examples, collagen secretion granules. The paper emphasizes the value of electron microscopy, supporting an appropriate histological picture and immunophenotype, in identifying these relatively low-grade sarcomas.

Intranodal myofibroblastoma: report of a case

Palisaded myofibroblastoma (hemorrhagic spindle cell tumor) is a recent addition to the group of benign primary spindle cell lesions of lymph nodes. These tumors are characterized histologically by hemorrhage, palisading, and foci of collagen called amianthoid fibers. We report a further typical example with the aim of discussing its differentiation. Tumor cells were positive for smooth-muscle actin and vimentin. The cytoplasm contained moderate numbers of rough endoplasmic reticulum cisternae and some smooth-muscle type myofilaments. Subplasmalemmal densities and plasmalemmal caveolae, as well as material interpreted as external lamina, were identified at the cell surface, whereas the fibronexus junctions typical of myofibroblasts were not seen. Immunostaining for type IV collagen was positive. Intranodal myofibroblastomas have largely been considered as myofibroblastic, but the observations presented here raise the alternative possibility of simple smooth-muscle differentiation. The foci of collagen widely referred to as amianthoid fibers contained fibrils mostly of conventional diameter, 50-83 nm. The giant collagen fibrils typical of true amianthoid change were absent. It is suggested that the term amianthoid be used only after ultrastructural confirmation of the presence of giant collagen fibrils.

Brief review of the fibronexus and its significance for myofibroblastic differentiation and tumor diagnosis

This brief review details the structure, nature, and distribution of the fibronexus, and discusses its significance for myofibroblastic differentiation and tumor diagnosis. The fibronexus is a cell surface specialization consisting of intracellular actin filaments and extracellular fibronectin filaments associated with subplasmalemmal plaque material. The fibronexus represents an intercellular junction between myofibroblasts, but in particular is a device for providing contact between myofibroblasts and matrix that mediates continuity between intracellular contractile filaments and extracellular matrix proteins. Immunoelectron microscopy in particular has shown that the intracellular filaments contain actin. The extracellular filaments contain fibronectin and collectively form the fibronectin fibril. The plaque probably contains such proteins as vinculin, talin, alpha-actinin, and integrin. Under appropriate biologic development and fixation conditions, the fibronectin fibril of the fibronexus is characterized by and distinguished from lamina by enhanced density, a rigid appearance, failure to adhere closely to the contours of the cell surface (except focally near the plaque material), and a longitudinally filamentous substructure. Confirmation of the presence of a fibronectin fibril may be obtained by the finding of intense cell surface staining with an antifibronectin antibody. Problems in identifying the fibronexus may be encountered, however, due to poor development and fixation, in which case the filamentous substructure may be inapparent. The fibronexus is such a typical feature of and is often so conspicuous in myofibroblasts that it can be regarded as perhaps essential for the interpretation of myofibroblastic differentiation. Structures with a similar appearance have been documented in fundamentally nonmyofibroblastic cells; these include aortic and scleral spur smooth muscle cells and endothelium. Uncertainties remain in the protein composition of the fibronexus, the nature of its contact with the matrix, and its relationship to similar structures seen in nonmyofibroblastic cells. Immunoelectron microscopy provides a potential means of clarifying some of these questions.

A study of spindle cell sarcomas showing myofibroblastic differentiation

Five diagnostically problematic spindle cell sarcomas showing invasive character, cellular pleomorphism, and high mitotic rate were studied clinically and histopathologically by conventional light microscopy, immunohistochemistry, and transmission electron microscopy. They showed varied clinical courses, with two causing death within 5 years and three showing recurrent and metastatic behavior. All lacked a clearly defined line of differentiation by conventional light microscopy. By immunohistochemistry, all were positive for vimentin and alpha-smooth muscle actin; in addition, one showed focal S-100 protein positivity, and one stained for desmin. All were cytokeratin negative. By electron microscopy, the great majority of spindle cells in all cases showed abundant rough endoplasmic reticulum and fine myofilaments with focal densities; collagen secretion granules were also found in all cases but in fewer cells. The fine structure and immunophenotype were considered consistent with myofibroblastic differentiation; these tumors, therefore, were designated as sarcomas of myofibroblasts or myofibrosarcomas. The suitability of the alternative diagnostic label of myofibroblastic or matrix-secreting variant of leiomyosarcoma is discussed. Comparisons with similar tumors documented in the literature are drawn.