Expansion of vitiligo lesions is associated with reduced epidermal CDw60 expression and increased expression of HLA-DR in perilesional skin

BACKGROUND: Detection of CDw60 in skin is representative of ganglioside D3 expression. This ganglioside is expressed primarily by melanocytes, and is of interest as a membrane antigen targeted by immunotherapy for melanoma patients. Expression of CDw60 by keratinocytes is defined by the presence of T-helper cell (Th)1 vs. Th2 cytokines, and can serve as a sentinel molecule to characterize an ongoing skin immune response. OBJECTIVES: These immunobiological characteristics have provided the incentive to study the expression of CDw60 in the context of progressive vitiligo. METHODS: Frozen sections were obtained from control skin and from vitiligo lesions and immunostained to show CDw60. Cells were cultured, their CDw60 expression studied and ribonuclease protection assays run to detect cytokine mRNA. RESULTS: Resistance to cytokine-mediated regulation of CDw60 expression was demonstrated in vitro by melanocytes, which appeared capable of generating autocrine and paracrine regulatory molecules supporting CDw60 expression. Induction of CDw60 expression was inhibited by antibodies to interleukin (IL)-4, suggesting that this cytokine was responsible, at least in part, for melanocyte-induced CDw60 expression. Marginal skin from patients with progressive generalized vitiligo consistently showed a reduction in epidermal CDw60 expression alongside elevated human leucocyte associated antigen (HLA)-DR expression at the margin. It thus appears that inflammatory infiltrates present in marginal skin generate type 1 rather than type 2 cytokines, supportive of a cell-mediated autoimmune response. CONCLUSIONS: These results support an active role of melanocytes within the skin immune system, and associate their loss in generalized vitiligo with a cell-mediated immune response mediated by type 1 cytokines.     

Cancer cell expression of urokinase-type plasminogen activator receptor mRNA in squamous cell carcinomas of the skin

In this study we have used in situ hybridization with radiolabeled antisense RNA probes to examine the expression of mRNA for urokinase-type plasminogen activator and its receptor in histologic samples of squamous cell (n = 7) and basal cell (n = 7) carcinomas of the skin. Messenger RNA for both urokinase-type plasminogen activator and its receptor were expressed in all of the squamous cell carcinomas, but could not be detected in the basal cell carcinomas. In all of the seven squamous cell carcinomas a signal for urokinase-type plasminogen activator receptor mRNA was detected focally in well-differentiated cancer cells surrounding keratinized pearls, and in four specimens urokinase-type plasminogen activator receptor mRNA was in addition expressed by cancer cells at the edge of invasively growing strands of tumor. Urokinase-type plasminogen activator mRNA expression was found in virtually all the cancer cells of the squamous cell carcinomas, and importantly we found, by hybridizations for urokinase-type plasminogen activator and its receptor mRNA on adjacent sections of squamous cell carcinomas, that it was exactly the invading cancer cells that simultaneously expressed both these components required for plasmin-mediated proteolysis at the cell surface. We have previously shown that both urokinase-type plasminogen activator and its receptor mRNA are expressed by the leading-edge keratinocytes in regenerating epidermis during mouse skin wound healing, and that wound healing is impaired in mice made deficient in plasminogen by targeted gene disruption. We propose that there are similarities between the mechanisms of generation and regulation of extracellular proteolysis during skin re-epithelialization and squamous cell carcinoma invasion. The ability of the squamous carcinoma cells to mimic the "invasive" phenotype of re-epithelializing keratinocytes may be one of the factors that make squamous cell carcinomas more aggressive tumors than basal cell carcinomas.     

Expression of 38-kD cell-surface glycoprotein in transformed human keratinocyte cell lines, basal cell carcinomas, and epithelial germs

In this study, we attempted to identify and characterize transformation-induced cell-surface glycoproteins of human keratinocytes. Therefore, we first searched for glycoproteins which are significantly elevated in human keratinocytes after transformation and immortalization by SV40 virus and which are also found at high levels in keratinocytic cell lines derived from squamous cell carcinomas of the skin. Out of at least 80 different cell-surface antigenic systems of human tumor cells, only three glycoproteins showed elevated expression in transformed keratinocytes. Among these, a 38-kD glycoprotein (gp 38) was highly increased in all transformed keratinocyte cell lines tested, but was not elevated in transformed fibroblasts. The expression of gp 38 was further characterized in normal epidermis and in its benign and malignant hyperproliferative disorders: gp 38 was generally not expressed in normal epidermis and in benign hyperproliferative disorders. In contrast, strong and homogeneous reactivity was found in solid and fibrosing basal cell carcinomas whereas no or low reactivity was detected in squamous cell carcinomas and in those parts of BCC revealing keratotic differentiation. Interestingly, high expression of gp 38 was also found in primary epithelial germs of fetal skin, secondary germ cells of the telogenic hair follicle and secretory tubules of sweat glands. The immunohistologic data suggest that gp 38 is preferentially expressed by epidermal cells which lack squamous and pilosebaceous differentiation.     

Expression of class II beta-tubulin in non-melanoma cutaneous tumors

BACKGROUND: Different combinations of beta-tubulin isotypes contribute to the diverse functions of microtubules (MTs). Class II beta-tubulin (class II tubulin) is up-regulated in differentiated keratinocytes. In contrast, the expression of class II tubulin in follicular differentiation and cutaneous tumors has not been studied. METHODS: The immunohistochemical expression of class II tubulin was investigated in 117 cutaneous tumors: 30 squamous cell carcinomas (SCCs), seven keratoacanthomas (KAs), 57 basal cell carcinomas (BCCs), 23 trichoepitheliomas (TEs), and in the adjacent non-neoplastic skin. RESULTS: Class II tubulin was expressed in the keratinocytes of the granular layer, melanocytes, hair cortical and cuticular cells, inner root sheath (IRS), companion layer (CL) of the outer root sheath (ORS), and mesenchymal cells with Schwannian or myogenic differentiation. Moreover, class II tubulin expression was increased in the areas of squamous or follicular differentiation in cutaneous tumors. On grading the follicular differentiation or myofibroblastic response with anti-class II tubulin, TE showed follicular differentiation more frequently (p < 0.001) with less of a myofibroblastic response (p = 0.001) than BCC. CONCLUSIONS: Class II tubulin expression is closely related to squamous or follicular differentiation and may be helpful in distinguishing most SCCs from KAs and BCC from TE. However, it does not reliably distinguish well-differentiated, crateriform SCC from KA.     

Expression of vascular endothelial growth factor in normal epidermis, epithelial tumors and cultured keratinocytes

Vascular endothelial growth factor (VEGF), an endothelium-specific growth factor and microvessel hypermeability factor, is expressed and secreted by several kinds of cells and is implicated in angiogenesis of tumors. The present study was performed to determine the relationship between the expression of VEGF in normal skin, benign and malignant epithelial lesions and cultured keratinocytes and the proliferative activity and degree of differentiation of keratinocytes. Skin lesions were studied immunohistochemically by staining with two anti-VEGF antibodies and secretion and production of VEGF by keratinocyte cultures were evaluated using an enzyme-linked immunosorbent assay. Low to moderate VEGF expression was observed in normal epidermis. In epithelial tumors, different reactivity patterns were observed and different areas of the same tumor expressed different amounts of VEGF. A more prominent labelling occurred in proliferative layers and/or more differentiated cells of virus-induced lesions, squamous cell carcinomas and Bowen’s disease, whereas basal cell carcinomas always stained weakly for VEGF. In cultured keratinocytes, the amount of cell-associated and secreted VEGF increased with time, and the constitutively produced VEGF was mostly released extracellularly. High calcium concentrations upregulated the intracellular content of VEGF but downregulated its release. Taken together, these results showed a modulated expression and release of VEGF in relation to the stage of cell differentiation and in rapidly growing or activated keratinocytes. Received: 22 April 1996     

Tissue Distribution of a Melanoma-Associated Antigen Immunogenic in Patients with Melanoma as Analyzed by Polyclonal Antibodies to Recombinant Peptide Antigen

This study aimed to detect in vivo expression of human melanoma-associated antigen D-1, which was identified by screening an expression cDNA library constructed from mRNA extracted from cultured melanoma cells with sera from patients with melanoma. The tissue distribution of D-1 antigen was then analyzed. Murine anti-D-1 recombinant peptide polyclonal antibodies were raised by immunization of in vitro synthesized D-1 peptide against Balb/c mice and applied immunohistochemically on paraffin-embedded tissue specimens. D-1 antigen was found to be restrictedly expressed on melanoma cells, but not on normal melanocytes, adjacent keratinocytes, fibroblasts, lymphocytes and adnexal structures of skin. The reactivities of anti-D-1 antibodies did not correlate with histogenesis of the lesions, their ability to produce melanin, and/or their primary or metastatic nature. There was no positive reactivity of anti-D-1 antibodies with other skin tumors, including squamous cell carcinoma, basal cell epithelioma, seborrheic keratosis, and nevus cell nevus. Further, cytoplasmic expression of D-1 antigen in melanoma cells was observed only in a certain subgroup of patients with melanoma. This indicates that the cell surface expression of D-1 peptide requires specific transporting proteins, such as HLA molecules.     

Expression of human macrophage metalloelastase (MMP-12) by tumor cells in skin cancer

Matrix metalloproteinases play an essential role in tumor growth and invasion. Different matrix metalloproteinases are often expressed in cancers with distinct patterns. To investigate the role of human macrophage metalloelastase (MMP-12) in epidermal tumors, we studied human macrophage metalloelastase mRNA and protein expression in malignant squamous cell and basal cell carcinomas, and in premalignant Bowen's disease. Human macrophage metalloelastase was detected in 11 of 17 squamous cell carcinomas in epithelial cancer cells, whereas macrophages were positive in 15 of 17 samples. In basal cell carcinomas, human macrophage metalloelastase was more often found in macrophages (seven of 19) than in cancer cells (four of 19). Human macrophage metalloelastase mRNA was also detected in three cell lines derived from squamous cell carcinomas of the head and neck and in transformed HaCaT cells, whereas premalignant tumors and primary keratinocytes were negative for human macrophage metalloelastase mRNA. Western analysis revealed human macrophage metalloelastase protein in squamous cell carcinoma cells. Our results show that human macrophage metalloelastase can be expressed in vivo and in vitro by transformed epithelial cells and indicate that the level of human macrophage metalloelastase expression correlates with epithelial dedifferentiation and histologic aggressiveness.     

Role of Integrins in Cell Adhesion and Polarity in Normal Keratinocytes and Human Skin Pathologies

In vitro, normal human keratinocytes reconstitute a differentiated stratified epidermis, maintaining the same gene expression pattern as its in vivo counterpart and are suitable for permanent grafting onto patients. Keratinocyte adhesion to basal lamina and lateral interactions among basal epidermal cells are also mediated by integrin receptors that are sorted to defined plasma membrane domains. The hemidesmosome-associated integrin α₆β₄ is sharply localized at the basal surface of basal cells and codistributes with laminin and nicein/kalinin; the α₂β₁ and α₃β₁ integrins are enriched laterally and play crucial roles in cell-cell interaction and proper colony morphology. During wound healing, proliferating and migrating keratinocytes express on their plasma membrane α_vβ₅ and α₅β₁, which allow keratinocyte attachment and migration over the provisional matrix present in the wound. TGFβ, which is an autocrine and paracrine mediator in wound healing, specifically increases the synthesis and expression of α_vβ₅ and α₅β₁, induces the de novo expression of α_vβ₆, and determines the loss of integrin polarization. In hyperproliferative skin diseases, such as skin cancer or psoriasis vulgaris, and in normal keratinocytes forced into more frequent cell cycles, the polarized expression of integrins is lost, and α₅β₁ becomes costitutively expressed on the plasma membrane. In addition, the α₆β₄ integrin becomes associated with focal contacts. Nerve growth factor (NGF) is a potent autocrine stimulator of keratinocyte growth and induces melanocyte migration toward the leading edge of a healing wound. We are currently investigating the NGF-dependent modulation of integrin expression and function in keratinocytes and melanocytes in both normal epidermis and several hyperproliferative skin diseases.     

Distribution of neu (c-erbB-2) protein in human skin

The neu (c-erbB-2) gene encodes a transmembrane protein with tyrosine kinase activity that appears to be a growth factor receptor. Antibody was generated by immunization of rabbits with a synthetic polypeptide that was based on an internal sequence at the carboxy terminus of the molecule. This antibody was used to survey the expression of neu in human skin by immunohistochemistry. Significant protein was found in the squamous cell layer of the surface epidermis, in squamous cell carcinomas, in the external root sheath of hair follicles, and in eccrine gland secretory cells; it was poorly expressed in the basal cell layer and in a basal cell carcinomas. Increased neu expression appears to be associated with the differentiation of keratinocytes.     

Expression Profile of CD10, BCL-2, p63, and EMA in the Normal Skin and Basal Cell Carcinomas: An Immunohistochemical Reappraisal

BackgroundBasal cell carcinoma (BCC) is common cutaneous malignancy.AimsTo examine the expression patterns of CD10, p63, BCL-2, and epithelial membrane antigen (EMA) proteins in BCC.Materials and methodsWe used immunohistochemistry to evaluate the expression pattern of these proteins in 45 BCC specimens and their adjacent normal skin.ResultsWe found variations in the expression pattern of these proteins among normal skins and BCC. In normal skins, we found strong EMA cytoplasmic expression (adnexal structures). A strong nuclear p63 protein expression was found in basal and some suprabasal keratinocytes, external root sheath cells of the hair follicles, basal cells of the sebaceous glands, and in sweat glands.CD10 protein expression was seen in peri-adnexal mesenchymal spindle cells and myoepithelial cells of sweat glands.BCL-2 protein expression was confined to the basal cell keratinocytes, epidermal melanocytes, outer root sheath, and infundibulum of the hair follicle. In BCC, we found p63 (diffuse, strong nuclear staining), CD10 (focal, moderate cytoplasmic reactivity), and BCL-2 (focal, moderate cytoplasmic reactivity) protein expression in the neoplastic cells. BCC was consistently negative for EMA (except in areas of squamous differentiation).ConclusionsThere is an altered expression of these proteins in BCC. The underlying molecular mechanisms are open to further investigations.     

Ceramide potentiates, but sphingomyelin inhibits, vitamin D-induced keratinocyte differentiation: comparison between keratinocytes and HL-60 cells

Abstract Differentiation of epidermal keratinocytes and leukemia HL-60 cells induced by 1,25-dihydroxyvitamin D [1,25(OH)₂D] has been reported to be mediated, at least in part, by increases in cellular ceramide levels. Ceramides produced by 1,25(OH)₂D-induced sphingomyelin (SM) hydrolysis also contribute to the permeability barrier lipids in keratinocytes. Exogenously supplied SM is taken up by mammalian cells, including keratinocytes, and is incorporated into cellular pools. However, the effects of exogenously added SM on keratinocyte differentiation have not been studied. Therefore, in this study, we compared exogenously added SM with a cell-permeable ceramide for their ability to stimulate keratinocyte differentiation induced by 1,25(OH)₂D. Both short-chain ceramide (C2-cer) and SM stimulated the differentiation and inhibited the proliferation of HL-60 cells. As expected, this effect was potentiated by 1,25(OH)₂D. However, SM inhibited the differentiation and stimulated the proliferation of keratinocytes. While C2-cer potentiated the effects of 1,25(OH)₂D, SM reversed the effects of 1,25(OH)₂D on keratinocytes. The ratio of SM to ceramide was significantly different between keratinocytes and HL-60 cells. While the SM level of HL-60 cells were twice that of keratinocytes, keratinocytes contained ten times more ceramides than HL-60 cells, resulting in a ceramide/SM ratio 17 times higher in keratinocytes. Thus, we identified similarities and significant differences in the sphingolipid-mediated cell signaling pathway between keratinocytes and HL-60 cells. While SM stimulated HL-60 cell differentiation, presumably by incorporation into SMase-accessible membrane pools, it inhibited keratinocyte differentiation. In keratinocytes, SM was possibly incorporated into a different cellular pool (barrier lipid pool) or altered membrane phospholipid metabolism and membrane fluidity. Received: 12 August 1998 / Received after revision: 5 November 1998 / Accepted: 6 November 1998     

Keratoacanthoma: A deficient squamous cell carcinoma? Study of bcl-2 expression

Ten keratoacanthomas with both proliferative and regressive histologic features along with 10 well-differentiated squamous cell carcinomas were examined using immunohistochemistry for the expression of bcl-2, a protooncogene recently recognized to be involved in protecting cells from undergoing apoptosis. The squamous cell carcinomas had a modest but diffuse staining pattern, while the proliferative keratoacanthomas stained only at the basal cells and only rare cells stained positively in the regressive keratoacanthomas. The degree and pattern of staining suggest a loss of bcl-2 expression with tumor maturity in keratoacanthoma and a possible role in their ultimate involution. Sleater JP, Beers BB, Stephens CA, Hendricks JB. Keratoacanthoma: A deficient squamous cell carcinoma? Study of bcl-2 expression.     

Detecting expression of keratins 8/18 in human HaCaT keratinocytes

Differences in treatment solution affect the efficiency of keratin extraction in cultured human squamous cell carcinomas, malignant melanomas, and melanocytes. Using an aqueous solution that is excellent for cultured cells, we focused this study on the expression of keratin subunits in the spontaneously immortalized human keratinocyte cell line HaCaT. We extracted several keratin (K) subunits, namely K4, K7, K8, K15, K17, and K18, and ATP synthase alpha-chain, in addition to those previously reported by Boukamp et al. (J Cell Biol 1988;106:761-771) in human HaCaT keratinocytes. In particular, K8 and K18 subunits, which are related to tumorigenesis, may be very important subunits within the specificities of immortalized HaCaT cells. Vimentin, which is frequently co-expressed in cultured epithelial cell lines, was not expressed.     

Cytochemical expression of epidermal peroxidase and cytochrome oxidase activities in pathological skin conditions of man

Summary The cytochemical expression of epidermal peroxidase and cytochrome oxidase activity was recently well documented in normal human skin.We report here its expression in basal and squamous cell carcinomas, actinic keratoses, psoriasis, allergic contact dermatitis, seborrheic keratoses, and autosomal dominant ichthyosis vulgaris. The two enzyme activities were evaluated using the diaminobenzidine method. If present, the two enzymes were always localized in the same organelles as in normal epidermis endogenous peroxidase in the nuclear envelope and endoplasmic reticulum, and cytochrome oxidase in mitochondria. In basal and squamous carcinomas, actinic keratoses and psoriasis, the keratinocytes lost their peroxidase activity, but maintained their cytochrome oxidase activity. In seborrheic keratoses, allergic contact dermatitis and ichthyosis vulgaris, the cytochrome oxidase activity was greatly reduced or abolished in keratinocytes, Langerhans' cells, and melanocytes, whereas the peroxidase activity was present as in normal epidermis. These results indicate that the two peroxidatic enzymes studied are not interrelated and alternatively suppressed by different cellular dysfunctions.A part of this work was presented at the combined 12th SCUR Annual Meeting and 6th International Dermatopathology Colloqium, April 1985, Florence, Italy     

Expression of BMI-1 in normal skin and inflammatory and neoplastic skin lesions

BACKGROUND: BMI-1 is involved in the maintenance of stem cells and functions as an oncogene in both lymphomas and solid carcinomas, acting by downregulation of p16ink4a. We have investigated the expression profile of BMI-1 in normal and inflamed skin as well as in basal cell carcinomas (BCCs) and squamous cell carcinomas (SCCs). METHODS: BMI-1 expression was determined by immunohistochemistry and immunofluorescence, and evaluated semiquantitatively. RESULTS: BMI-1 was weakly expressed in nuclei of basal and sometimes suprabasal keratinocytes, in basal cells of sebaceous glands, weakly to moderately in the bulge area and the external root sheath of hair follicles, and strongly in sweat glands. Whereas BCCs showed strong and diffuse BMI-1 expression, SCCs expressed BMI-1 heterogeneously. Strong cytoplasmic expression of BMI-1 was found in dividing cells. CONCLUSIONS: BMI-1 expression marks stem cells within the hair follicle. As BMI-1 was also found in suprabasal keratinocytes and a variety of specialized cells, the distribution of BMI-1 only partly reflects the known distribution of stem cell compartments. BMI-1 is strongly overexpressed in BCCs, tumors linked to dysregulation of the sonic hedgehog pathway, which has been shown to upregulate BMI-1, suggesting a contribution of the BMI-1 oncogene in their pathogenesis.     

Basal-cell adhesion molecule (B-CAM) is induced in epithelial skin tumors and inflammatory epidermis, and is expressed at cell-cell and cell-substrate contact sites

Basal-cell adhesion molecule (B-CAM) is a 90 kDa cell surface glycoprotein of the immunoglobulin superfamily that functions as a laminin-binding receptor. B-CAM is upregulated following malignant transformation of some cell types in vivo and in vitro, thus being a candidate molecule involved in tumor progression. As cutaneous distribution and function of B-CAM are largely unknown, we have studied its expression and regulation in normal and diseased human skin. In normal skin, B-CAM was expressed by endothelial cells of dermal blood vessels. In contrast, B-CAM was strongly upregulated within the tumor tissue of both malignant and benign epithelial skin tumors, including basal cell carcinomas, squamous cell carcinomas, keratoacanthomas, and common warts. Transformation-associated upregulation was confirmed in vitro, but normal keratinocytes also expressed B-CAM under culture conditions. Interestingly, the basal epidermal layer of normal-appearing skin surrounding the tumors also expressed B-CAM, and B-CAM were induced on the basal and apicolateral surfaces of basal keratinocytes in inflammatory skin disorders suggesting transformation-independent mechanisms of epidermal induction of the B-CAM. Immunoelectron microscopy studies of cultured transformed keratinocytes revealed that B-CAM was expressed at cell-cell and cell-substrate contact sites. Halting proliferation of transformed keratinocytes through cytostatic drugs resulted in decreased B-CAM synthesis. Likewise, inducing terminal differentiation in keratinocyte cultures by increasing the Ca(2+) concentration in the medium decreased B-CAM expression. In contrast, both ultraviolet A and B irradiation of cultured human keratinocytes resulted in significantly increased expression of the B-CAM. Overall, it appears that B-CAM expression in human skin is associated with activated states of keratinocytes, and that B-CAM may be involved in cell-cell adhesion or migration, in addition to its known function as a laminin receptor. J Invest Dermatol 115:1047-1053 2000     

Immunohistochemical evaluation of epidermis overlying basal cell carcinomas

We have examined the character and carcinogenic properties of the normal-appearing epidermis overlying basal cell carcinomas by immunohistochemical methods, employing a series of monoclonal antibodies. The labelling index was significantly increased in the atrophic epidermis overlying basal cell carcinomas (solid type, n=20). compared with the epidermis overlying or adjacent to squamous cell carcinoma (n=20). keratoacanthoma (n= 10). dermatofibroma (n=10), neurofibroma (n= 10). soft fibroma (n=10). pyogenic granuloma (n=10) and cutaneous leiomyoma (n=5). Cells which expressed epidermal growth factor (EGF) receptor were detected in all layers of the epidermis over the basal cell carcinomas, hut not the other tumours. Basement membrane-related antigens, including bullous pemphigoid antigen and GB3 antigen, were decreased in the epidermis. AEl. the monoclonal antibody against basal cell keratin, reacted with the uppermost layers of the normal-appearing epidermis overlying the basal cell carcinomas. ICAM-1 expression was very weak in the overlying epidermis. The dermis subjacent to the proliferating epidermis showed staining for transforming growth factor-α (TGF-α). strong positive PECAM-1 staining of endothelium. and numerous HLA-DR-positive cells. From these results, we suggest that the proliferative activity in the epidermis overlying basal cell carcinomas is not a state induced by the dermal infiltrate, but represents carcinogenic activity of the epidermis.     

Immunohistochemical comparison of beta-catenin expression by human normal epidermis and epidermal tumors

beta-Catenin, a cytoplasmic protein that binds directly to the intracellular domain of cadherin, controls various functions such as cell adhesion. In many human carcinomas, E-cadherin-mediated cell-cell adhesion is lost or disturbed and related to metastasis. The purpose of this study was to compare the expression of beta-catenin in the normal epidermal keratinocytes and samples from cutaneous benign and malignant epidermal tumors in 140 patients. Our study population consisted of 140 patients with benign or malignant epidermal tumors. Using immunohistochemical methods, we compared the expression of beta-catenin in their normal epidermal keratinocytes, and in samples from 61 benign (seborrheic keratosis, n = 33; verruca vulgaris, n = 14; keratoacanthoma, n = 14), and 79 malignant (Bowen's disease, n = 18; basal cell carcinoma, n = 33; squamous cell carcinoma, n = 28) epidermal tumors. beta-Catenin was found to be expressed in the cell membrane of normal keratinocytes. Compared to other cell components of the normal epidermis, basal cells showed the strongest beta-catenin expression in all 140 patients. While absent in three of 61 benign tumors, compared to normal basal cells, the expression of beta-catenin in the other 58 tumors was not significantly different; it was reduced in 71 of 79 malignant tumors (P < 0.0001). In Bowen's disease, the expression of beta-catenin on the tumor cell membrane was reduced, however, strong expression was seen in the nuclei and cytoplasm. Our results suggest that beta-catenin expression on the membrane of keratinocytes is associated with the differentiation of normal keratinocytes but not with their stage of differentiation, nor with the proliferation ability of epidermal tumor cells.