Fibroblast activation protein: differential expression and serine protease activity in reactive stromal fibroblasts of melanocytic skin tumors

Growth and metastasis of solid neoplasms require the recruitment of a supporting tumor stroma. A highly consistent trait of tumor stromal fibroblasts in most epithelial cancers is the induction of fibroblast activation protein (FAP), a member of the serine protease family. Recently it was demonstrated that FAP has both dipeptidyl peptidase and collagenolytic activity capable of degrading gelatin and type I collagen. In this study, we describe the expression and enzyme activity of FAP in benign and malignant melanocytic skin tumors. FAP-positive fibroblasts were detected immunohistochemically in the reactive stroma of all melanocytic nevi tested. In primary and metastatic melanomas an upregulation of FAP expression in the reactive mesenchyme could be observed. Whereas 30% of the nevi revealed additional FAP expression on subsets of melanocytic cells, melanoma cells from primary and metastatic melanomas were FAP negative. This may indicate a possible role for FAP in the control of tumor cell growth and proliferation during melanoma carcinogenesis. Consistent with this in vivo expression pattern FAP enzyme activity could be detected by a specific immunocapture assay in extracts of melanocytic nevi and melanoma metastases, whereas no significant activity was detectable in normal adult skin. Strong protein expression of FAP was observed in patterned structures restricted to a subset of the melanoma metastases. Our findings that these FAP-positive structures showed no overlap with endothelial cell surface markers, nor with various melanoma antigens, suggest that FAP is a marker for specific stromal-cell-derived patterns in cutaneous melanoma metastases.     

Tubulin expression in melanocytic skin tumors. An immunohistochemical study

The microtubulus system as a part of the cellular cytoskeleton contributes to cell movement. Microtubulus assembly and disassembly is considered to be essential for tumor invasion and serves as a target for tumor chemotherapy. Using immunohistochemical methods, we investigated the distribution of tubulin in normal skin and 34 melanocytic skin tumors. In normal skin, tubulin was strongly expressed in dermal nerves, melanocytes, fibroblasts within the papillary dermis and in myoepithelial cells. In melanocytic skin tumors, nevus cells and melanoma cells stained positive, particularly at the periphery of the lesions, where there were single cells and small nests. The main difference between benign and malignant melanocytic tumors was found in the stromal cells: In melanocytic nevi, the stromal fibroblasts were entirely tubulin negative; whereas, adjacent to the invasive edge in primary and metastatic malignant melanoma, the stroma fibroblasts were strongly positive. Our results show that tubulin is regularly expressed in melanocytic skin tumors and may serve as a prerequisite for cell movement. The pronounced expression of tubulin in fibroblasts surrounding malignant melanocytic skin lesions reflects a stromal alteration that might contribute to tumor invasion.     

Expression of cytoskeletal components in melanocytic skin lesions. An immunohistochemical study

The cytoskeleton is considered to be important for maintaining cell shape and facilitating cell movement. In the present study, the expression of cytoskeletal components is examined in benign and malignant melanocytic skin tumors. Paraffin sections of 75 cases (25 each of nevocellular nevus, primary malignant melanoma, and cutaneous metastases of malignant melanoma) were stained with antibodies to tubulin, myosin, actin, and vimentin using a three-step immunoperoxidase method. The staining results were assessed independently for tumor cells and stroma cells in comparison to inbuilt reference structures. Vimentin is found in all melanocytic lesions in the tumor as well as in the stroma cells. In malignant lesions, the tumor cell staining intensity varies between neighboring regions; particularly in malignant melanoma the staining is pronounced in the tumor periphery (chi 2 test: p less than 0.05). Actin is only weakly positive in nevus cells and primary melanoma tumor cells, but strongly expressed in metastatic tumor cells (p less than 0.001). Nevus fibroblasts are only weakly positive, whereas the stroma fibroblasts in the malignant lesions are strongly positive (p less than 0.001). The same is true for myosin and tubulin expression in dermal fibroblasts (p less than 0.001), whereas the tumor cells are equally (weakly) positive in all melanocytic lesions. Our study shows that there are significant differences in the immunohistochemical expression of cytoskeletal components in various melanocytic tumors. There is an elevated expression of vimentin and actin in the tumor cells, particularly of metastatic lesions. However, the most pronounced differences are found in the dermal fibroblasts.(ABSTRACT TRUNCATED AT 250 WORDS)     

Desmoplastic leiomyosarcoma of the skin

This report focuses on two unusual cases of cutaneous leiomyosarcoma composed of sparse numbers of neoplastic cells embedded in abundant sclerotic stroma throughout the entire neoplasm. To the best of our knowledge, only one example of this rare lesion has been described previously as "sclerotic primary cutaneous leiomyosarcoma." However, the resemblance of this tumor to other desmoplastic tumors of the skin is striking and, therefore, we propose the term desmoplastic leiomyosarcoma of the skin for this neoplasm. Because of the sparse cellularity and the abundant stroma, desmoplastic leiomyosarcoma of the skin can be easily misinterpreted, especially in small biopsies. It should be included in the differential diagnosis of inflammatory skin diseases associated with sclerosis, such as radiation dermatitis, and of desmoplastic tumors of the skin, including desmoplastic melanocytic nevus, desmoplastic melanoma, and desmoplastic squamous cell carcinoma.     

Multicellular origin of tenascin in skin tumors – an in situ hybridization study

Tenascin mRNA expression was studied by an in situ hybridization method in 27 skin tumors. Tenascin synthesis was increased in all skin tumors when compared to uninvolved skin but there was variation in the site of cellular synthesis between different types of tumors. In melanocytic nevi and precancerous keratinocyte lesions, tenascin seemed to be of epidermal or stromal origin. In basal cell carcinoma, squamous cell carcinoma and malignant melanoma, there was tenascin synthesis also in tumor cells. These findings are in concordance with earlier studies which suggest a role of tenascin as an anti-adhesive and motility-promoting factor in malignant skin tumors.     

Nerve growth and expression of receptors for nerve growth factor in tumors of melanocyte origin.

Nerve growth factor (NGF) stimulates growth and differentiation of sensory and sympathetic neurons. It is not known what role NGF plays in melanoma development, but nevus and malignant melanoma cells express NGF-receptor (NGF-R). We counted nerve fibers within melanocytic nevi, primary cutaneous melanomas, and cutaneous melanoma metastases using a monoclonal antibody (MoAb) as marker against a 200-kD glycoprotein that is expressed on human nerves. The expression of NGF-R was studied in serial cryostat sections using a MoAb against the NGF-R. Compared to normal skin, increased numbers of nerve fibers were found in 72 melanocytic nevi. In congenital nevi their number significantly increased with age. In 47 primary cutaneous melanomas the number of nerve fibers decreased in proportion to tumor thickness. In 33 cutaneous melanoma metastases no accumulation of nerve fibers was found. NGF-R was not expressed in normal skin melanocytes and in the majority of nevus cells in melanocytic nevi. Considerable numbers of NGF-R-positive nervus cells were found only in some congenital nevi and few acquired nevi with dysplastic features. By contrast, in primary and metastatic melanomas higher expression of NGF-R was observed. The increased number of nerve fibers in melanocytic nevi suggests that neurite-promoting factors are produced in situ. Production of such factors appears to be lost in malignant melanoma cells. The finding of an inverse correlation between an abundance of nerve fibers in NGF-R-poor nevi and a high expression of NGF-R in melanomas that show no evidence of nerve growth suggest a role of NGF and its receptor in malignant melanocytic tumors.     

Controversial role of mast cells in skin cancers

Cancer development is a multistep process characterized by genetic and epigenetic alterations during tumor initiation and progression. The stromal microenvironment can promote tumor development. Mast cells, widely distributed throughout all tissues, are a stromal component of many solid and haematologic tumors. Mast cells can be found in human and mouse models of skin cancers such as melanoma, basal and squamous cell carcinomas, primary cutaneous lymphomas, haemangiomas and Merkel cell carcinoma. However, human and animal studies addressing potential functions of mast cells and their mediators in skin cancers have provided conflicting results. In several studies, mast cells play a pro‐tumorigenic role, whereas in others, they play an anti‐tumorigenic role. Other studies have failed to demonstrate a clear role for tumor‐associated mast cells. Many unanswered questions need to be addressed before we understand whether tumor‐associated mast cells are adversaries, allies or simply innocent bystanders in different types and subtypes of skin cancers.     

Value of p63 and podoplanin (D2‐40) immunoreactivity in the distinction between primary cutaneous tumors and adenocarcinomas metastatic to the skin: a clinicopathologic and immunohistochemical study of 79 cases

The distinction of metastatic carcinomas to the skin from poorly differentiated primary cutaneous carcinomas and sometimes primary benign adnexal tumors can pose a significant diagnostic challenge. The purpose of this study was to evaluate the role of p63 and podoplanin (D2‐40) immunoreactivity for separating primary skin tumors vs. cutaneous metastases of carcinomas from internal organs. Thirty seven primary tumors and 42 cutaneous metastatic adenocarcinomas were evaluated. The 37 primary cutaneous tumors included 14 cases of benign adnexal tumors, 9 malignant skin adnexal neoplasms, and 14 primary squamous and basal cell carcinomas. The 42 metastatic adenocarcinomas all corresponded to metastases from patients with a well‐documented history of a primary tumor at another location. We found variable positivity with podoplanin in all primary cutaneous neoplasms including spiradenoma (6/6), hidradenoma (2/4), cylindroma (3/3), desmoplastic trichilemmoma (1/1), poorly differentiated squamous cell carcinoma (4/4), sebaceous carcinoma (1/1), basal cell carcinoma (4/10), trichilemmal carcinoma (2/2), eccrine carcinoma (3/3), microcystic adnexal carcinoma (1/1), adnexal carcinoma NOS (1/1), and porocarcinoma (1/1). In contrast, all metastatic carcinomas were negative (0/42) for podoplanin. In regards to p63, all cases of primary cutaneous tumors were positive for p63 (37/37); in contrast, all cutaneous metastatic carcinomas were negative (0/42). Sensitivity, specificity, and positive and negative predictive values of podoplanin and p63 immunoreactivity to separate primary skin neoplasms from metastatic carcinomas were 78.4, 100.0, 100.0 and 84.0% for podoplanin, respectively, and 100.0, 100.0, 100.0 and 100.0% for p63, respectively. The differences in p63 and podoplanin immunohistochemical expression between primary skin tumors and metastatic carcinomas to the skin were statistically significant (p < 0, 0001). The results of our study suggest that the combined expression of p63 and podoplanin are a useful adjunct for the diagnosis of skin tumors in the clinical setting of a questionable metastasis and may be relatively specific for distinguishing primary skin tumors from metastatic carcinomas to the skin. Plaza JA, Ortega PF, Stockman DL, Suster S. Value of p63 and podoplanin (D2‐40) immunoreactivity in the distinction between primary cutaneous tumors and adenocarcinomas metastatic to the skin: a clinicopathologic and immunohistochemical study of 79 cases.     

Laminin‐5 Expression in Melanocytic Lesions of the Skin

Background: Laminin‐5 is a basement membrane constituent that functions as an anchoring filament to integrin‐derived hemidesmosomes, and has been detected at the invasive front (tumor‐stromal interface) in many types of carcinomas. Our goal was to analyze laminin‐5 expression in melanocytic lesions and evaluate its role in tumor progression. Design: Immunohistochemical staining for laminin‐5 was performed on 101 cutaneous melanocytic lesions including 41 nevi, 31 primary melanomas, and 29 metastatic melanomas. A standard immunoperoxidase technique (ABC) was used with DAB chromagen and a primary monoclonal antibody to the laminin‐5 gamma2 chain (clone D4B5, 1:50, Chemicon International, Temecula, CA). Any degree of staining in melanoma cells or at the tumor‐stromal interface was considered positive. Results: Positive staining for laminin‐5 was observed in three of the primary melanomas (10.7%), three of the metastatic melanomas (10.3%), and none of the nevi. In primary melanomas, staining was observed predominately at the tumor‐stromal interface. In metastatic lesions, staining was observed around individual melanoma cells and melanoma cell nests.Conclusion: Expression of laminin‐5 was detected in a small percentage of primary and metastatic melanomas and in none of the nevi studied. Laminin‐5 expression does not appear to be essential for the development of melanomas or their metastases.     

骨桥蛋白在黑素瘤中的表达

目的研究骨桥蛋白(OPN)的表达与黑素瘤浸润、转移的关系。方法采用免疫组化SP法检测OPN在黑素瘤(30例)、黑素细胞痣(30例)、正常皮肤组织(15例)以及在黑素瘤A375细胞株和不同浓度乙酰肝素酶反义寡核苷酸转染的裸鼠黑素瘤移植瘤中的表达。结果 OPN在黑素瘤、黑素细胞痣及正常皮肤组织中阳性表达率分别为86.67%(26/30),13.33%(4/30)和0(0/15),黑素瘤组与黑素细胞痣组及正常皮肤组OPN的阳性表达率比较差异有统计学意义(P=0.000)。3种不同浓度的乙酰肝素酶反义寡核苷酸在转染的裸鼠体内恶性黑素瘤移植瘤中表达表现出不同程度的抑制作用,30μmol/L实验组的抑制作用最强。OPN在人黑素瘤A375细胞株中呈强阳性表达。结论 OPN在黑素瘤中的表达明显高于其在黑素细胞痣和正常皮肤中的表达;乙酰肝素酶反义寡核苷酸对裸鼠体内黑素瘤移植瘤中OPN的表达有显著抑制作用;OPN在A375细胞株中呈强阳性表达。     

Primary cutaneous adenosquamous carcinoma: a case report and review of the literature

BACKGROUND: Adenosquamous carcinoma (ASC) of skin is a rare but distinctive neoplasm that usually exhibits an aggressive course. To date, 13 well-documented and undisputed cases of primary cutaneous ASC have been reported. This term has been used for tumors with better prognosis, such as mucoepidermoid carcinomas and acantolytic squamous cell carcinomas, originating confusion. We report a primary cutaneous ASC and review the literature. METHODS: In this report a woman with primary ASC of the skin was studied. Histopathological examination and immunohistochemical stains were performed. RESULTS: The tumor had two components: conventional squamous cell carcinoma merging with adenocarcinoma. After a local recurrence and lymph node metastases, the patient has no evidence of disease 8 months later. CONCLUSIONS: Pathologists should reserve the term ASC for tumors exhibiting the above mentioned appearance. In such circumstances, a metastatic origin must always be excluded.     

PTEN expression in normal skin, acquired melanocytic nevi, and cutaneous melanoma

BACKGROUND: Although various studies have shown mutations of the tumor suppressor gene, PTEN/MMAC1, in primary, metastatic, and cultured cutaneous melanoma specimens, little is known about the pattern of PTEN protein expression in early melanocytic tumor progression. OBJECTIVE: To further investigate the role of PTEN in melanocytic tumor development. METHODS: We assessed the level and distribution of PTEN in normal skin, 39 acquired melanocytic nevi, and 30 primary cutaneous melanomas, including lentigo malignas, by immunostaining. RESULTS: We found high levels of PTEN expression in cutaneous muscles, nerves, and muscular arteries, and moderate-to-high amounts of PTEN in the epidermis, follicular epithelium, and sebaceous and eccrine glands. PTEN staining in cutaneous lymphatics, dermal and periadnexal adventitial fibroblasts, and chondrocytes were variably absent. Junctional melanocytes and chondrocytes frequently exhibited preferential nuclear staining. We found uniformly strong PTEN expression in the cytoplasm of almost all benign and dysplastic nevi. However, there was some evidence of nuclear PTEN loss even in the benign melanocytic proliferations. In addition, out of 30 primary cutaneous melanomas and lentigo malignas, we detected diffuse expression of PTEN in 11 (37%) tumors, widespread loss of PTEN in 11 (37%) tumors and mixed PTEN expression in 8 (27%) lesions. In the primary cutaneous melanomas, PTEN was largely localized to the cytoplasm. CONCLUSIONS: The presence of PTEN in benign melanocytic tumors and the absence of PTEN in a significant proportion of primary cutaneous melanomas support a role for PTEN loss in the pathogenesis of melanoma.     

MEL4B3, a novel mRNA is induced in skin tumors and regulated by TGF-beta and pro-inflammatory cytokines

Tumor-stroma interactions play a decisive role in the growth and metastasis of solid tumors, and involve signalling either by soluble mediators or direct cell-cell interaction. Here, we report the isolation and characterisation of a novel cDNA (MEL4B3), which is induced in cultured dermal fibroblasts exposed to supernatants of melanoma cell lines. MEL4B3 shares high homology with two predicted cDNA sequences for which no activity has so far been described. In situ hybridisation revealed the expression of MEL4B3 in malignant melanoma increasing with tumor depth; in basal cell carcinoma and in squamous cell carcinoma. MEL4B3 was barely detectable in normal skin or non-malignant melanocytic naevi. Furthermore, MEL4B3 was expressed at high level in the epidermis of psoriatic skin. In vitro, the expression of MEL4B3 was found to be induced by the exposure of human dermal fibroblasts to melanoma cell culture supernatants or to transforming growth factor-beta, interleukin-1 and tumor necrosis factor-alpha. The expression MEL4B3 therefore reflects closely cell activation occurring during tumor growth, metastasis and inflammation.     

Loss of p14<Superscript>ARF</Superscript> expression in melanoma

Lack of p14ARF expression or its functional inactivation has been observed in human and murine carcinomas. Although very few mutations of p14ARF have been detected in some cancer types, changes in expression seem to play an important role in the development of other human cancers such as mesotheliomas. To examine the p14ARF gene and expression of p14ARF protein in melanomas, we screened eight human melanoma cell lines and primary human melanocytes by RT-PCR, sequencing and immunoblotting. All melanoma cell lines analyzed expressed wild-type p14ARF mRNA as well as protein. P14ARF expression was investigated by immunohistochemical staining of 32 tissue samples of benign melanocytic nevi (n=14), melanomas (n=12) and melanoma metastases (n=6). In contrast to the results obtained from cell lines in vitro the immunohistochemical stainings revealed a correlation between the progression of melanoma and the lack of the p14ARF protein expression. Positive p14ARF protein staining was observed in 11 of 14 benign nevi, in 3 of 12 melanomas and in 0 of 6 melanoma metastases. In summary, we demonstrated a significant inverse correlation between p14ARF protein expression and progression of melanocytic tumors since the amount of p14ARF protein staining decreased from benign melanocytic nevi to metastatic melanoma in situ. These results suggest that p14ARF inactivation is important in the development of melanomas.     

Expression of galanin in melanocytic tumors

IntroductionGalanin is a neuropeptide with wide-ranging effects, especially within the endocrine and nervous systems. Galanin and its receptors are present in human skin. Galanin is expressed in different neural, endocrine and neuroendocrine tumors and, on the other hand, several neuropeptides, particularly α-MSH, seem to play a role in the pathogenesis of melanoma.ObjectiveTo investigate the expression of galanin in cutaneous melanomas and melanocytic nevi and correlate it with α-MSH expression and several prognostic factors for melanoma.Material and methodsWe performed an observational and retrospective study of the immunohistochemical expression of galanin and α-MSH in samples of cutaneous melanomas diagnosed in the last 5 years in the San Jorge Hospital, Huesca (Spain). Different types of melanocytic nevi were also analyzed.ResultsA total of 130 pigmented lesions were studied: 38 primary cutaneous melanomas, 6 cutaneous melanoma metastases and 86 melanocytic nevi. Immunostaining with galanin and α-MSH was significantly higher in melanomas than in melanocytic nevi (p < 0.001), although spindle cell and blue nevi showed significant expression of α-MSH. More than 50 % of nodular melanomas and 90 % of superficial spreading melanomas were positive for galanin and α-MSH, and the latter also showed the highest percentage of positive cells for galanin (mean 35.09 ± 28.16) as well as for α-MSH (mean 67.64% ± 35.38). A positive correlation of 71 % was found for immunostaining of both neuropeptides in melanomas. No significant correlation was observed between galanin expression and age, gender, location of the lesions, Breslow index, Clark level and mitotic index.ConclusionOur study shows the expression of galanin in cutaneous melanoma and its significant correlation with α-MSH immunostaining.     

CD44 and melanocytic tumors: a possible role for standard CD44 in the epidermotropic spread of melanoma

CD44 is a polymorphic family of cell membrane glycoproteins that mediate cell-matrix and cell-cell interactions involved in the mechanisms of tumor invasion and metastasis, and are subject to differential regulation during normal and malignant cell growth. We have investigated immunohistochemically the expression of CD44S and the variant isoforms CD44v3 and CD44v6 in paraffin-embedded tissue from 5 Spitz nevi, 3 compound melanocytic nevi, 2 blue nevi, 6 primary melanomas, 15 cutaneous metastases (three epidermotropic, nine dermal and three ulcerated) and 10 lymph node metastases of melanoma. Melanocytes were extensively positive for CD44S in primary melanomas and benign melanocytic proliferations. Among 15 cases of cutaneous metastases of melanoma, the three epidermotropic metastases, as well as one of the three ulcerated ones were positive for CD44S. CD44S expression was diminished or totally absent in six of the nine dermal metastases, in two of the ulcerated metastases and in seven of the ten lymph node metastases. CD44v3 and CD44v6 melanocytic expression was absent in all the lesions studied.
According to our results, selective retention of CD44S expression by melanocytes in epidermotropic metastases of melanoma seems to indicate that preservation of CD44S may contribute to the intraepidermal spread of melanoma.     

Melanocytes express 3G5 surface antigen

The 3G5-reactive ganglioside antigen (3G5 antigen) is expressed on the surface of various cell types including pericytes, pancreatic islet cells, thyroid follicular cells, and cells of the pituitary and the adrenal medulla. Expression on melanocytes has not yet been reported. We examined 148 5-microm cryosections of 12 normal skin samples and 45 skin tumors (21 melanocytic nevi, 8 malignant melanoma primaries, 4 metastases of malignant melanoma, 3 basal cell carcinomas, and 9 pigmented seborrheic keratoses) by triple fluorescence technique with the monoclonal antibody 3G5, DNA fluorochrome, and the anti-melanocytic antibody A103 (Anti-Melan-A). In normal skin, 3G5 reactivity was detected in epidermal melanocytes of 4 of 12 cases with 14.8 +/- 24.1% positive melanocytes; 20 of 21 nevi (72.2 +/- 29.1% positive nevus cells, mean +/- SD), 8 of 8 primary melanomas (83.9 +/- 12.3% positive melanoma cells), and 4 of 4 melanoma metastases (82.5 +/- 6.5% positive melanoma cells) expressed the 3G5 antigen. All tumor cells of investigated basal cell carcinoma or seborrheic keratosis were 3G5 negative. This is the first report of 3G5 antigen expression in melanocytes. The data demonstrate high expression of this ganglioside in the aggregated melanocytes of malignant or benign tumors but low or absent expression in singular melanocytes (normal epidermis, seborrheic keratoses) reflecting a different biologic state.     

Thrombospondin-1 and Cutaneous Melanoma

BACKGROUND: Thrombospondins (TSPs) are recognized as important glycoproteins that regulate a wide variety of cell functions and interactions. TSPs in malignant tumors can both enhance and inhibit tumor progression, invasion, and metastasis, depending on cell type, stromal interactions, and microenvironment. These proteins are potential targets for anticancer therapy. OBJECTIVE: The aim of our article is to review the role of thrombospondin-1 (TSP1) in cutaneous melanoma. CONCLUSIONS: TSP1 expression is variable in melanoma cell lines and tumors. Similar to findings in other human cancers, expression of TSP1 by melanoma cells usually inhibits tumor progression via the antiangiogenic effect of TSP1. Conversely, stromal TSP1 overexpression in melanoma is a poor prognostic factor associated with decreased survival. Understanding the interactions of TSP1 with other melanoma- and matrix-associated proteins should provide new prognostic indices and possible therapeutic targets for melanoma treatment.     

Expression of purinergic receptors in non-melanoma skin cancers and their functional roles in A431 cells

We investigated the use of purinergic receptors as a new treatment modality for nonmelanoma skin cancers. Purinergic receptors, which bind adenosine 5'-tri-phosphate, are expressed on human cutaneous keratinocytes. Previous work in rat and human epidermis suggested functional roles for purinergic receptors in the regulation of proliferation, differentiation, and apoptosis. Immunohistochemical analysis of frozen sections in human basal cell carcinomas and squamous cell carcinomas for P2X5, P2X7, P2Y1, P2Y2, and P2Y4 receptors was performed, accompanied by detailed analysis of archive material of tumor subtypes in paraffin sections. Functional studies were performed using a human cutaneous squamous cell carcinoma cell line (A431), where purinergic receptor subtype agonists were applied to cells and changes in cell number were quantified via a colorimetric assay. Immunostaining in paraffin sections was essentially the same as that in frozen sections, although more detail of the subcellular composition was visible. P2X5 and P2Y2 receptors were heavily expressed in basal cell carcinomas and squamous cell carcinomas. P2X7 receptors were expressed in the necrotic center of nodular basal cell carcinomas and in apoptotic cells in superficial multifocal and infiltrative basal cell carcinomas, and squamous cell carcinomas. P2Y1 receptors were only expressed in the stroma surrounding tumors. P2Y4 receptors were found in basal cell carcinomas but not in squamous cell carcinomas. P2X5 receptors appear to be associated with differentiation. The P2X7 receptor agonist benzoylbenzoyl-adenosine 5'-triphosphate and high concentrations of adenosine 5'-triphosphate (1000-5000 microM) caused a significant reduction in A431 cell number (p<0.001), whereas the P2Y2 receptor agonist uridine 5'-triphosphate caused a significant amount of proliferation (p<0.001). We have demonstrated that non-melanoma skin cancers express functional purinergic receptors and that P2X7 receptor agonists significantly reduce cell numbers in vitro.