Fibroepithelioma of Pinkus is a true basal cell carcinoma developing in association with a newly identified tumour-specific type of epidermal hyperplasia.

BACKGROUND: Fibroepithelioma of Pinkus (FEP) has long been viewed as a subtype of basal cell carcinoma (BCC). Recently, however, the proposal has been made that FEP represents a fenestrated trichoblastoma/trichoepithelioma. One of the main arguments is the presence of Merkel cells in FEP, which typically do not occur in BCC. OBJECTIVES: As the new stem cell marker, PHLDA1 (TDAG51), labels trichoepithelioma but not BCC, our aim was to characterize its staining pattern in FEP. Because adnexal tumours have been viewed as recapitulating embryogenesis, we also examined PHLDA1 immunoreactivity in the skin of human embryos and fetuses. METHODS: We studied immunohistochemically PHLDA1 staining in 31 FEPs, 14 BCCs and 16 trichoepitheliomas and compared this with its staining pattern in embryonic skin and with the distribution of Merkel cells. RESULTS: In FEP, PHLDA1 labels the anastomosing network of thin cellular strands but not the basaloid nubbins. During embryogenesis, PHLDA1 stains the basal cell layer of the epidermis, as long as adnexal structures develop. Immunoreactivity for PHLDA1 correlates positively with the presence of Merkel cells. CONCLUSIONS: We propose that the thin anastomosing network of PHLDA1-positive cells represents a type of epidermal hyperplasia specific to FEP. The multifocal BCCs that are PHLDA1-negative develop from this network which becomes incorporated into the tumour. Viewing the anastomosing network as a tumour-specific form of epidermal hyperplasia explains the hitherto enigmatic presence of Merkel cells in FEP.

[Basal cell carcinoma and stem cell markers : Contribution to possible histogenesis?]. / Basalzellkarzinom und Stammzellmarker : Beitrag zur möglichen Histogenese?

The prevalence and incidence of basal cell carcinoma are on the rise. Yet, its histogenesis is still controversial. Hitherto discussed concepts are largely based on morphological analogies. Historically, basal cell carcinoma was named after its similarity to the epidermal basal cell layer which is viewed as its histogenetic origin. On the other hand, a primitive follicular origin is postulated due to the morphological similarity of basal cell carcinoma to the embryonic hair germ. In 1990, the hair follicle bulge was characterized as the anatomical niche for follicular stem cells. Early studies employing stem cell markers suggested a follicular origin of basal cell carcinoma. Since then an explosion of stem cell markers has occured in dermatology. In this review, the stem cell markers employed in the examination of basal cell carcinoma up to now are critically evaluated. Initially, studies on the histogenesis of this common dermatological tumor are reviewed.

Basal cell carcinoma: cell of origin, cancer stem cell hypothesis and stem cell markers.

Cancer stem cells have recently been described in several high-grade neoplasms. It is still unclear if they also occur in cutaneous malignancies. Cancer stem cells are not identical with somatic stem cells. The presence of tumour stem cells in a neoplasm does not in itself equal that the tumour derives from a somatic stem cell. A cell originally lacking stem cell characteristics could also acquire those features during the course of carcinogenesis and then becomes the clonal founder cell of a tumour. Basal cell carcinoma (BCC) is the most common cutaneous malignancy. A plethora of various stem cell markers has been applied to study its cellular origin. Intriguingly, the anatomical origin of BCC is still uncertain. This review will discuss the various stem cell markers used in BCC and the cellular origin of this tumour, and touches briefly on the possibility of cancer stem cells in BCC. If BCC or other skin cancers harbour tumour stem cells, these cells could be specifically targeted, making use of specific cell surface molecules such as receptor proteins. Novel drugs directed against those receptor proteins could replace currently available shotgun approaches including imiquimod.

PHLDA1 (TDAG51) is a follicular stem cell marker and differentiates between morphoeic basal cell carcinoma and desmoplastic trichoepithelioma.

BACKGROUND: Morphoeic basal cell carcinoma (BCC) and desmoplastic trichoepithelioma can often be difficult to differentiate on routine sections and few reliable immunohistochemical markers are currently available. Recent cDNA microarray studies revealed the pleckstrin homology-like domain, family A, member 1 protein (PHLDA1) as a highly reliable marker of the hair follicle stem cells. Given the differentiation of trichoepithelioma along the follicular lineage and the proposed role of PHLDA1 as a follicular stem cell marker, we examined the staining pattern of PHLDA1 in the desmoplastic variant of trichoepithelioma and in its differential diagnostic conundrum, morphoeic BCC. OBJECTIVES: To describe the expression pattern of PHLDA1 in morphoeic BCC and desmoplastic trichoepithelioma. METHODS: Evaluation of the staining pattern for PHLDA1 was performed using standard immunohistochemical techniques. For comparison reasons, we analysed staining for PHLDA1 in normal skin structures with particular reference to the hair follicle. RESULTS: With the exception of one case, all 16 desmoplastic trichoepitheliomas were immunoreactive with more than 80% of the cells stained, whereas all 14 morphoeic BCCs were PHLDA1-negative with the exception of ulcerated tumours. In the latter, the tumour islands close to the ulcer were PHLDA1-positive whereas the deeper located tumour portions remained immunonegative. PHLDA 1 was prominently expressed in the hair follicle bulge of terminal and vellus hair follicles. CONCLUSIONS: The hair follicle bulge marker PHLDA1 differentiates between desmoplastic trichoepitheliomas and nonulcerated examples of morphoeic BCCs. We suggest incorporating PHLDA1 in the diagnostic work-up of difficult to differentiate basaloid tumours.

[Cutaneous mesenchymal stem cells. Current status of research and potential clinical applications]. / Mesenchymale Stammzellen der Haut. Gegenwärtiger Stand der Forschung, potenzielle klinische Anwendungen.

Within the next decade stem cell-based therapies can be expected to be part of clinical medicine. In regard to the skin, the focus of stem cell research is on the epidermis and the hair follicle. In 2001, mesenchymal stem cells residing within the dermis were first isolated which have the capacity to differentiate into adipocytes, smooth muscle cells, osteocytes, chondrocytes and even neurons and glia as well as hematopoietic cells of myeloid and erythroid lineage. The perifollicular connective tissue sheath and the papilla represent the likely anatomical niche for these multipotent dermal cells. They have the potential to function as an easily accessible, autologous source for future stem cell transplantation. Potential therapeutic applications include the treatment of acute and steroid-refractory graft-versus-host disease, systemic lupus erythematosus, idiopathic pulmonary fibrosis and arthritis. The neuronal differentiation potential of cutaneous mesenchymal stem cells may also be exploited in the treatment of neurodegenerative disorders and traumatic spinal injury. The most immediate impact can be expected in the field of wound healing.

p75 Neurotrophin receptor differentiates between morphoeic basal cell carcinoma and desmoplastic trichoepithelioma: insights into the histogenesis of adnexal tumours based on embryology and hair follicle biology.

BACKGROUND: Tumour development is frequently described in the basic pathology literature as a recapitulation of embryogenesis. However, a link between the embryology of the skin and the histogenesis of adnexal tumours has been largely overlooked. The low-affinity p75 neurotrophin receptor (p75NTR) has a profound role in hair follicle biology. We therefore speculated that it is involved in the histogenesis of follicular adnexal tumours. One of the most challenging diagnoses in dermatopathology is differentiating morphoeic basal cell carcinoma from desmoplastic trichoepithelioma. OBJECTIVES: To describe the expression pattern of p75NTR during cutaneous embryogenesis, in the adult hair follicle and in morphoeic basal cell carcinoma and desmoplastic trichoepithelioma. METHODS: Evaluation of the staining pattern for p75NTR was performed using standard immunohistochemical techniques. For comparison, we examined staining for cytokeratin 20 which highlights Merkel cells. RESULTS: All 17 desmoplastic trichoepitheliomas were immunoreactive with > 80% of the cells stained, whereas 12 of the 14 (86%) morphoeic basal cell carcinomas were p75NTR negative. In the two positive cases of morphoeic basal cell carcinoma < 30% of cells were labelled. In the late bulbous hair peg stage and in the postnatal anagen hair follicle p75NTR highlights the outer root sheath. CONCLUSIONS: Our results support the classification of desmoplastic trichoepithelioma as a follicular hamartoma mimicking the outer root sheath. In contrast, the lack of p75NTR expression in morphoeic basal cell carcinoma favours a concept of this tumour as a more primitive follicular lesion with the characteristics of a carcinoma and not a hamartoma. We suggest including p75NTR as a tool in the differential diagnosis between morphoeic basal cell carcinoma and desmoplastic trichoepithelioma.

Basal cell carcinoma and pilomatrixoma mirror human follicular embryogenesis as reflected by their differential expression patterns of SOX9 and ß-catenin.

BACKGROUND: The current classification schemes of adnexal tumours are predominantly based on morphological and immunophenotypical similarities to adult skin structures, whereas a link between the embryology of the skin and the histogenesis of adnexal tumours has been largely neglected. OBJECTIVE: To describe the expression patterns of two proteins with proven relevance for hair follicle homeostasis (SOX9 and ß-catenin) during human cutaneous embryogenesis and to compare the findings with their expression in basal cell carcinoma (BCC) and pilomatrixoma. METHODS: Immunohistochemical evaluation with monoclonal antibodies against SOX9 and ß-catenin was carried out in embryonic and adult human scalp skin, and BCC and pilomatrixoma samples. RESULTS: We found that the expression patterns of SOX9 and ß-catenin during human hair follicle embryogenesis mirror the patterns in BCC and pilomatrixoma in spatial distribution within the various follicular subcompartments. Beginning with the hair peg stage, nucleocytoplasmic immunoreactivity of ß-catenin is exclusively confined to the emerging matrix (comparable to pilomatrixoma), whereas SOX9 is restricted to the primordial outer root sheath (comparable to BCC). CONCLUSIONS: An appropriate immunophenotyping validated within the conceptual framework of cutaneous developmental biology allows a logical classification of adnexal neoplasms. Expanding this approach further has the potential to revise the current classification schemes so that not only BCC and pilomatrixoma but all adnexal tumours can be categorized logically.

Dermatofibrosarcoma protuberans: a tumour of nestin-positive cutaneous mesenchymal stem cells?

BACKGROUND: There is an increasing body of evidence suggesting that malignancies arise from mutated stem cells, which has led to the formulation of the cancer stem cell hypothesis. It has also been suggested that cutaneous malignancies originate from a mutated stem cell. To date, mesenchymal tumours of the skin have not been the focus of the cancer stem cell hypothesis. A population of mesenchymal stem cells has recently been identified in the dermal compartment of the skin. These proposed stem cells are positive for the neuroepithelial stem cell marker nestin. OBJECTIVES: To describe the expression pattern of nestin, a neuroepithelial stem cell protein, in dermatofibrosarcoma protuberans (DFSP). METHODS: Immunohistochemical evaluation of DFSP with a monoclonal antibody against nestin was performed using standard techniques. For comparison we also analysed dermatofibromas (DF). In addition, we used antibodies against CD34 and Factor XIIIa; the proliferation marker Ki67 was also used. RESULTS: Strong immunoreactivity for nestin was found in DFSP whereas all DF cases were nestin-negative. CONCLUSIONS: We propose that DFSP may represent a clonal expansion of a nestin-positive mesenchymal stem cell which would put this tumour in line with other neoplasms for which the cancer stem cell hypothesis was formulated. We suggest the use of nestin as an additional marker for DFSP, especially in cases of negative immunoreactivity for CD34. Nestin may also be employed for margin evaluation of DFSP in micrographic (Mohs) surgery.

The neuroepithelial stem cell protein nestin is a marker of the companion cell layer of the adult and developing human hair follicle.

BACKGROUND: The interface between the inner root sheath (IRS) and the outer root sheath (ORS) represents a slippage plane for the hair shaft to evolve from the pilar canal to the skin surface. Interposed between the IRS and ORS is a single cell layer which is believed to represent the angle point of that slippage plane, termed the companion cell layer (CCL). The CCL is cited in most of the literature as part of the ORS. OBJECTIVES: To describe the expression pattern of nestin, a neuroepithelial stem cell protein, in the adult and developing human hair follicle. METHODS: Immunohistochemical evaluation with a monoclonal antibody against nestin was performed using standard techniques. RESULTS: Nestin is selectively expressed in the CCL of the adult anagen and late stage fetal hair follicles. Early stages of hair follicle development are negative for nestin expression. CONCLUSIONS: The selective demarcation of the CCL by nestin highlights the unique feature of this follicular cell layer and raises the question of whether the CCL should not be better conceptualized as a part of the IRS rather than the ORS. The results of the present study, together with published ultrastructural data, also suggest that the slippage plane for the evolving hair shaft may be located at the interface between the CCL and the ORS.

What causes hidradenitis suppurativa?

Hidradenitis suppurativa (HS)--a rather common, very chronic and debilitating inflammatory skin appendage disorder with a notoriously underestimated burden of disease--has long been a playground for the high priests of nomenclature: Ask a bunch of eminent dermatologists and skin pathologists to publicly share their thoughts on what causes HS, and they will soon get entrenched in a heated debate on whether this historical term is a despicable misnomer. Fortunately, the recently founded Hidradenitis Suppurativa Foundation (HSF; http://www.hs-foundation.org), to which EXP DERMATOL serves as home journal, has broken with this unproductive tradition and has encouraged publication of the current CONTROVERSIES feature. This is exclusively devoted to discussing the pathobiology of this chronic neutrophilic folliculitis of unknown origin. Although traces of terminological bickering remain visible, it does the HS experts in our virtual debate room credit that they engage in a constructive and comprehensive dissection of potential pathogenesis pathways that may culminate in the clinical picture we know under the competing terms HS or acne inversa. These experts sketch more often complementary than mutually exclusive pathogenesis scenarios, and the outlines of a conceivable consensus on the many open pathobiology questions begin to emerge in these CONTROVERSIES. Hopefully, this heralds a welcome new tradition: to get to the molecular heart of HS pathogenesis, which can only be achieved by a renaissance of solid basic HS research, as the key to developing more effective HS therapy.

Distribution of Bcl-2 and Bax in embryonic and fetal human skin: antiapoptotic and proapoptotic proteins are differentially expressed in developing skin.

The Bcl-2 protein is involved in the regulation of apoptosis. Bax has an antagonistic effect and enhances cell death. We report that in early gestation, Bcl-2 and Bax colocalize to the epidermal portion of the hair follicle. In the more advanced stages, Bax is located in the compartments where a hair canal is excavated and keratinization and holocrine secretion are initiated, in contrast to Bcl-2, which is expressed in the follicular papilla, preventing apoptosis and underscoring its role as a permanent and stable population of specialized fibroblasts. Scattered dendritic cells located in the basal and immediate suprabasal interfollicular epidermis as well as in the outer root sheath of the developing hair follicle, including the bulge, strongly express Bcl-2 and label for HMB-45, identifying them as melanocytes. The spatial and temporal expression pattern of Bcl-2 and Bax during human hair follicle development underscores their importance for hair biology and most likely is disturbed in the evolution of follicular tumors.

[Transgenic mice as models for skin diseases]. / Transgene Mäuse als Modelle für Hautkrankheiten.

Naturally occurring animal models are not available even for most common skin diseases. Transgenic technology developed during the 1980s is closing this gap. It was initially used as a tool by scientists in basic research, but during the last 5 years it has increasingly been applied by clinically oriented basic researchers in dermatology. This technique, has made it possible to imitate HIV-associated diseases and genodermatoses in the murine model and to elucidate their pathogenesis. Owing to specifically induced epidermally localized overexpression of growth factors and cytokines, the skin of transgenic mice exhibited similarities to those of the psoriatic epidermis. Such animals are also useful for studying wound healing. Furthermore, transgenic technology enables us to induce cutaneous tumors selectively. The availability of animal models for human skin diseases is also of value in elucidating experimental therapeutic approaches, e.g., the somatic gene therapy.

Multiple defects and perinatal death in mice deficient in follistatin.

Follistatin, an activin-binding protein and activin antagonist in vitro, can bind to heparan sulphate proteoglycans and may function in vivo to present activins to their receptors. In the mouse, follistatin messenger RNA is first detected in the deciduum (on embryonic day 5.5), and later in the developing hindbrain, somites, vibrissae, teeth, epidermis and muscle. In Xenopus laevis, overexpression of follistatin leads to induction of neural tissue. Here we use loss-of-function mutant mice to investigate the function of follistatin in mammals. We find that follistatin-deficient mice are retarded in their growth, have decreased mass of the diaphragm and intercostal muscles, shiny taut skin, skeletal defects of the hard palate and the thirteenth pair of ribs, their whisker and tooth development is abnormal, they fail to breathe, and die within hours of birth. These defects are more widespread than those seen in activin-deficient mutant mice, indicating that follistatin may modulate the actions of several members of the transforming growth factor-beta family.

Targeted overexpression of transforming growth factor alpha in the epidermis of transgenic mice elicits hyperplasia, hyperkeratosis, and spontaneous, squamous papillomas.

To assess the effects of transforming growth factor alpha (TGF-alpha) on mammalian skin in vivo, we have targeted its expression to the epidermis of transgenic mice using a vector based on the human K1 (HK1) gene. Neonatal mice expressing the HK1.TGF-alpha transgene were often smaller than normal littermates and had precocious eyelid opening and wrinkled, scaly skin with diffuse alopecia. Juvenile transgenic mouse epidermis was uniformly hyperkeratotic, but this pattern was generally less pronounced in adult transgenic mice unless they expressed high levels of the HK1.TGF-alpha transgene. Spontaneous, squamous papillomas occurred at sites of wounding in adult mice expressing high levels of HK1.TGF-alpha; however, most were prone to regression. Immunoreactive TGF-alpha was 2-6 times higher in the epidermis of these HK1.TGF-alpha lines. Immunoreactive epidermal growth factor receptor had a normal pattern of expression in nonphenotypic adult epidermis, but a marked reduction in the receptor population was detected in hyperplastic newborn epidermis and phenotypic adult epidermis. Autoradiographic localization of 125I-epidermal growth factor showed a similar pattern of distribution, suggesting that the sites of increased TGF-alpha expression induced epidermal growth factor receptor down-regulation. These data demonstrate the in vivo effect of deregulated TGF-alpha expression on epidermal proliferation and differentiation and suggest a potential role for TGF-alpha in carcinogenesis and other hyperproliferative epidermal disorders.

Transgenic models of skin diseases.

BACKGROUND: Transgenic animals have greatly enhanced our understanding of the contribution of various structural and regulatory components to epidermal biology. The expression of mutant versions of these components in the epidermis of transgenic mice has generated animal models of specific human skin diseases. OBSERVATIONS: The expression of mutant keratin genes has produced animal models of epidermolysis bullosa simplex and epidermolytic hyperkeratosis and, in doing so, has focused attention on the genetics of keratins in these and other skin disorders. Similarly, the generation of mice overexpressing growth factors and/or oncogenes, exclusively in the epidermis, has identified the role of these factors in normal skin and produced models of disease states where the regulation of these factors is perturbed. CONCLUSIONS: These models of keratin disorders and other diseases not only enable the determination of the cause of these disorders, but also allow evaluation of novel therapeutic techniques for the amelioration of these skin diseases.

Inhibition of skin development by overexpression of transforming growth factor beta 1 in the epidermis of transgenic mice.

To assess the effect of transforming growth factor beta 1 on the skin in vivo, we have targeted its expression to the epidermis of transgenic mice. To ensure that active TGF-beta 1 was expressed, we used a porcine TGF-beta 1 cDNA with mutations of Cys-223-->Ser and Cys-225-->Ser, which allow constitutive activation. Mice expressing the mutant transforming growth factor beta 1 transgene exhibited a marked phenotype at birth. The skin was very shiny and tautly stretched. These animals were rigid and appeared to be restricted in their ability to move and breathe; death occurred within 24 hr. Histologically, the most prominent features of the skin were a compact orthohyperkeratosis and a reduction in the number of hair follicles. Pulse-labeling studies with 5-bromodeoxyuridine demonstrated a marked reduction in the number of replicating cells in the epidermis and hair follicles. Thus, the macro- and microscopic appearance of these mice, as well as their neonatal lethality, most likely result from inhibition of normal skin development and suppression of epithelial cell proliferation by the overexpression of transforming growth factor beta 1.

Development of the choroid and related structures.

The development of the choriocapillaris and the choroid is described using light and electron microscopy. Up to the seventh week after conception, the endothelium of the choriocapillaris is thick and contains many cytoplasmic vesicles. By the ninth week the endothelium flattens and becomes vesiculated. Fenestrations are found as early as the seventh week, whereas the continuous basement membrane is only observed at the ninth week. The first choroidal arterioles and venules can be seen during the fifteenth week and the arteries and veins become distinguishable at the twenty-second week. Haller's and Sattler's layers are both venous and arterial at the time of their first appearance.

Isolation and antigenic profile of follicular dendritic cells.

Follicular dendritic cells (FDC) were isolated from human tonsils and adenoids. With a simple modification of an isolation method described previously, FDC could be enriched up to 50%. The isolated FDC were characterized immunocytochemically. In contrast to previous studies, CD4 antigen was not detected on freed FDC, thereby suggesting that the CD4 molecule does not play a role in the infection process of FDC in AIDS, as has been demonstrated for T helper cells. Fc receptors could not be found on FDC by the panel of monoclonal antibodies applied, whereas C3 receptors were observed in abundance. Therefore, antigen trapping in germinal centres most probably involves only C3 receptors. This concept is in contrast with the current one (also developed on isolated cells), which postulates the involvement of Fc receptors. The extent to which C3 receptors are involved in the pathogenesis of AIDS will be examined in further studies.

[Light and electron microscopy studies of the development of the human ciliary body]. / Licht- und elektronenmikroskopische Untersuchungen zur Entwicklung des menschlichen Ziliarkörpers.

In human embryos and fetuses with a gestation age of 9.5 to 24 weeks, differentiation of the ciliary muscle was examined by both light and transmission electron microscopy, and the surface morphology of the ciliary body was analyzed by scanning electron microscopy. Smooth muscle cells develop from mesenchymal elements or early fibroblasts located at the anterior rim of the optic cup. Musclelike cells exhibiting dense bodies and myofilaments were first distinguished during week 12 and smooth muscle cells with an adultlike appearance become apparent during week 15/16. A cellular maturation process can be observed up to week 22. Fibroblasts separating the muscle cell layers from each other also derive from the same precursor cells, as do smooth muscle cells, thereby pointing out the close relationship between the two cell types. The first radial ciliary folds could be observed at week 10.3 by scanning electron microscopy. However, true ciliary processes have only been described at week 24. The ciliary processes observed during week 24 only differed from those of the adult eye by the dimensions and lack of surface infoldings. A primitive pars plana was first identified during week 24. The morphological basis for aqueous humor production is discussed.