Dermatofibrosarcoma Protuberans and Dermatofibroma: Dermal Dendrocytomas? A Ultrastructural Study

Hugo Dominguez-Malagon, M.D., Ana Maria Cano-Valdez, M.D. Department of Pathology, Instituto Nacional de Cancerología, Mexico.

ABSTRACT population of plump spindled cells devoid of cell processes, these cells contained intracytoplasmic lipid droplets and rare Dermatofibroma (DF) and Dermatofibrosarcoma subplasmalemmal densities but lacked MVB. Protuberans (DFSP) are dermal tumors whose histogenesis has not been well defined to date. The differential diagnosis in most With the ultrastructural characteristics and the constant cases is established in routine H/E sections and may be confirmed expression of CD34 in DFSP, a probable origin in dermal by immunohistochemistry; however there are atypical variants dendrocytes is postulated. The histogenesis of DF remains of DF with less clear histological differences and non-conclusive obscure. immunohistochemical results. In such cases electron microscopy studies may be useful to establish the diagnosis. INTRODUCTION

In the present paper the ultrastructural characteristics of 38 The histogenesis or differentiation of cases of DFSP and 10 cases of DF are described in detail, the Dermatofibrosarcoma Protuberans (DFSP) and objective was to identify some features potentially useful for Dermatofibroma (DF) is controversial in the literature. For differential diagnosis, and to identify the possible histogenesis of DFSP diverse origins such as fibroblastic,1 fibro-histiocytic2 both neoplasms. Schwannian,3 myofibroblastic,4 perineurial,5,6 and endoneurial (7) have been postulated. DFSP in all cases was formed by stellate or spindled cells with long, slender, ramified cell processes joined by primitive junctions, Regarding DF, most authors are in agreement of a subplasmalemmal densities were frequently seen in the processes. histiocytic origin, but others propose the dermal dendritic Other common finding was the presence of Multi Vesicular cells.8 Buds (MVB). DFSP is a dermal tumor characterized by proliferation of In contrast, DF is characterized by proliferation of capillary spindled cells arranged in a fascicular or storiform pattern. vessels with prominent endothelium and a perivascular It features infiltration of adipose tissue creating a lace-like or honeycomb effect. Immuno-expression of CD34 is seen in almost 100% of cases.

Dermatofibroma is also a tumor of the dermis, formed of Key Words: Dermatofibroma, Dermatofibrosarcoma plump or spindle shaped cells arranged in a storiform pattern, Protuberans, Dermal Dendritic Cells. the tumor periphery is well defined and has a non-

Mailing address: Dr. Hugo Dominguez-Malagon, Department of Pathology, Instituto Nacional de Cancerología, Ave. San Fernando 22, Tlalpan, D.F., 14000, Mexico. E-mail: [email protected] Austral - Asian Journal of Cancer ISSN-0972-2556, Vol. 6, No.1, January 2007 9 Hugo Dominguez-Malagon infiltrating, “pushing” border, and the majority of cells express cells were wrapped around themselves or around capillary factor XIIIa. However, there are atypical types like the deep vessels in an “onion-skin” pattern or in a “radiating” pattern, variety,9 and the rare intermediate tumor that evidence a they were separated from the endothelium by basal lamina double population of cells expressing CD34 and F-XIIIa, In and normal pericytes. Mostly, the cell processes were these cases differences between DFSP and DF become delicately joined at their tips or at their sides by macula imprecise by immunohistochemistry,10 in such instances the adherens junctions (Fig 2). In a third of the cases the nuclei ultrastructural study could help in the differential diagnosis. has a convoluted shape with deep indentations (Fig 3), the chromatin in coarse granules arranged peripherally, nucleoli There are controversial points of view regarding the were not prominent Occasionally the nuclei showed a histogenesis of DFSP, and most ultrastructural studies include “blastic” appearance with dusty euchromatin, large nucleoli short series of cases.5,11,12 Concerning DF, electron and membrane blebs. In two thirds of cases peculiar microscopy studies are even more limited.8,13,14 For that structures called multivesicular buds MVB were found, those reason the aim of the present paper was to analyze a large consisted in bulbous projections of the cell membrane number of cases of DFSP to define the relevant abutting from the processes, inside of these buds there were ultrastructural characteristics and postulate possibilities for multiple small vesicles (Fig 4). In most cases there were its histogenesis. A more limited number of DF was studied scarce myofilaments with dense bodies and subplasmalemmal in an attempt to establish the ultrastructural differences with DFSP.

MATERIALS AND METHODS

Thirty-eight cases of DFSP and 10 cases of DF were studied by electron microscopy, All cases were chosen because their typical histological appearance and immunohistochemical studies positive for CD34 and Factor XIIIa respectively.

Immunohistochemical studies were performed using the avidin-biotin technique (CD34 and FXIIIa, Dako, Carpenteria CA, USA, 1:100).

For electron microscopy, tissue sections were fixed in 5% glutaraldehide, post-fixed in osmium tetroxyde, dehydrated Figure 1. Dermatofibrosarcoma Protuberans. Spindle-shaped cells in graded ethanol and embedded in epoxy resin. Fine with slender undulating processes alternating with lamellae of sections were contrasted with uranyl acetate and lead collagen fibers citrate. Observations were done in a Jeol 1010 electron microscope.

The general ultrastructural features were evaluated but some specific characteristics were selected: cell shape, nuclear shape, chromatin pattern, nucleolar appearance, intracytoplasmic lipid, subplasmalemmal densities, macula adherens junctions, myofilaments, anchoring fibers, pinocytic vesicles, and collagen fibers in the intercellular space. In addition the presence of special or previously undescribed details was registered.

RESULTS

Ultrastructurally DFSP was characterized by bipolar and multipolar cells with long, slender, ramified cytoplasmic processes arranged in parallel undulating layers that Figure 2. Dermatofibrosarcoma Protuberans. Spindle-shaped cell alternated with collagen layers (Fig 1). In some areas the with a deeply indented convoluted nucleus.

Austral - Asian Journal of Cancer ISSN-0972-2556, Vol. 6, No.1, January 2007 10 Dermatofibroma and Dermatofibrosarcoma Protuberans

Figure 3. The cells show interdigitated slender processes laterally Figure 5. In few cases of DFSP there were cells with joined by macula adherens junctions, there are subplasmalemmal myofibroblastic differentiation with peripheral myofilaments, densities and incomplete basal lamina. The cytoplasm contains subplasmalemmal densities and dilated RER cysternae, some RER cysternae and few lysosomes. with perimitochondrial arrangement. Well formed anchoring fibers (fibronexus) are seen (arrows)

Figure 4. Cell processes with “multivesicular buds” in DFSP, Figure 6. The cells of DF are oval or spindled with ample these structures are formed by bulbous cytoplasmic processes cytoplasm containing RER cysternae and lipid droplets. containing small vesicles densities (Fig 5). Other organelles constantly found were DISCUSSION rER cysternae and phagolysosomes. Rarely found structures were pinocytic vesicles, anchoring fibers (Fig 5) and In the majority of cases the diagnosis of DFSP is easily perimitochondrial rER. In the extracellular space there were established by routine histological study based in the storiform abundant mature and immature collagen fibers (Figs 1-5). pattern and infiltrating borders.9,18 and most cases of are positive for CD34 as in the present series. Dermatofibroma was characterized by ovoid or spindled neoplastic cells in close relationship to capillary vessels In constrast, DF is a small dermal tumor composed of showing plump endothelial cells. In one case there were spindled or plump cells arranged in a fascicular or storiform cell processes but no MVB were found. The cells had pattern with non infiltrating borders, and most cases are abundant cytoplasm containing rER cysternae and notably negative for CD34 but positive for FXIIIa.18a abundant lipids in form of cytoplasmic droplets or forming part of lipolysosomes (Fig 6). Other structures occasionally Despite these differences, both entities have histological found were: convoluted nuclei, subplasmalemmal densities variants that cause confusion between them and with other and myofilaments. tumors. DFSP may have abundant melanin pigment,3

Austral - Asian Journal of Cancer ISSN-0972-2556, Vol. 6, No.1, January 2007 11 Hugo Dominguez-Malagon myxoid pattern,16 and dedifferentiated areas of with dense bodies, anchoring fibers,29,30 intracellular collagen fibrosarcoma.17 DF may show atypia, pleomorphism, deep fibers31 and collagen secreting granules.32 location and recurrences.18 Recently, Horenstein et al.10 described a series of ten cases of dermal tumors with storiform The perineural and endoneural origin of DFSP has been pattern with a mixture of CD34 positive cells and F-XIIIa based in ultrastructural studies 5,6 since the cells have a positive cells, they had a benign course with exception of concentrical arrangement wrapping around themselves of one case that had a recurrence. The authors postulated around capillaries. However, perineural cells have other that these tumors represent intermediate forms of a spectrum characteristics not found in the present series like: composed of DF and DFSP. continuous basement membrane, pinocytic vesicles and randomly oriented intracytoplasmic microfilaments, in The results of the present paper allow the establishment of addition they are positive for EMA and negative for CD34. clear ultrastructural differences between these two entities. Endoneural cells are spindle-shaped randomly distributed DFSP is composed by dendritic cells with slender ramified in the endoneurium preferentially in the perivascular region, processes that frequently show subplasmalemmal densities they have phagocytic functions and are considered as the and MVB as described by Alguacil-Garcia.5 peripheral counterpart of microglia. These cells express CD34, however they do not show dendritic features and DF is formed by spindled or plump cells intimately related are ubiquitous, not exclusively found in the dermis as the to capillary vessels. The cells display abundant cytoplasm cells of DFSP. with lipid droplets and seldom display processes These findings are in agreement with some authors who have Other nominees are the dendritic dermal cells (DDC), observed a spectrum, with cells resembling fibroblasts at one these cells are the most dendritic cells outside central nervous end, and histiocytes at the other.13 Other authors have system, they have common histochemical and characterized the cells of DF as endothelial.14 In the present immunohistochemical features with the mononuclear series the cells were located in close relationship with phagocytic system and is probable that they form part of the capillary vessels but lacked endothelial characteristics. own immunocompetent system of the skin,34 and their ultrastructural characteristics are different from those of Most of the immunohistochemical studies published in mast cells, macrophages, pericytes, endothelium and the literature have demonstrated that the cells of DFSP fibroblasts. Some variants of DDC have been express vimentin and CD34,4,7,22 they are inconstantly characterized24,35,36 such as: perivascular dermal dendritic positive for actin,4 and negative for cytokeratin, epithelial cells (PDDC) located in proximity to the capillary vessels of membrane antigen (EMA), neurone-specific enolase, S100 papillary dermis, they express F-XIIIa and are negative for protein, desmin, HMB-45, F-XIIIa, alpha-1 antitripsin and CD34. Other DDC are found in the reticular dermis and myelin basic protein.1,4,19-21 subcutaneous tissue, they are also perivascular but not as close as PDDC, they express CD34 and are negative for F- CD34 is expressed in endothelial cells of small and newly XIIIa. formed blood vessels,23-25 it is also expressed in dendritic cells of reticular dermis located in proximity of blood vessels, The results of the present paper demonstrate that DFSP is eccrine ducts and perifollicular region.24 Endoneurial a tumor composed of dendritic cells. In support that these dendritic cells also express CD34. Tumors constantly positive cells may correspond to DDCs, is the fact that DFSP always for CD34 include: angiosarcoma, Kaposi’s sarcoma,24 has its initial presentation in the dermis, and is composed of epithelioid hemangioendothelioma,21 solitary fibrous a monotonous population of cells that constantly express tumor,26 gastrointestinal stromal tumors27 and DFSP; it is CD34. also expressed in dendritic cells of neurofibromas and in Anthoni B zones of Schwannomas. CD34 is negative in Regarding DF, the cells of this tumor have ultrastructural other nerve sheath tumors, fibroblastic tumors, muscular features of phagocytic and fibroblastic elements, and they tumors, neuroectodermal tumors and in lymphomas.7,21,22 are intimately related to blood vessels. A candidate for the origin of DF would be the PDDC as has been proposed by The histogénesis of DFSP as fibroblastic and Cerio et al.,8 however the ultrastructural features as shown myofibroblastic origin has been based in ultrastructural in the present paper give little support for this theory. studies and tissue culture,11,12 immunohistochemical studies,1,4 and the demonstration of fibronectin and collagen In conclusion, the ultrastructural features of DFSP and synthesis.28 In the present paper no reparative myofibroblasts DF permit to establish their differential diagnosis by electron were seen, these cells feature rER, peripheral myofilaments microscopy. DFSP is composed of CD34+ dendritic cells,

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