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Atypical melanocytic nevi constitute central risk factor and are precursor lesions for cutaneous melanoma. Data regarding factors associated with their prevalence are mainly derived from fair-skinned populations, whereas little is known regarding their epidemiological associations in darker-skinned, chronically sun-exposed populations. The aim of this study was to identify risk factors for the occurrence of at least one atypical nevus on Crete, the southernmost island of Greece. This hospital-based case-control study included 143 patients and 189 controls with at least one atypical nevus presented at the pigmented skin lesion clinic of the University of Crete. All participants were interviewed and underwent complete skin examination by the same two experienced dermatologists. Multivariate logistic regression analysis was used to adjust for potential confounders. In the multivariate analysis, common melanocytic nevi [odds ratio (OR): of 2.2, 7.5, and 58.9 for the presence of 11-25, 26-100, and >100 common nevi, respectively] and recreational sun exposure (OR: 4.4) increased significantly the risk of the presence of atypical nevus. A decreased risk for atypical nevi was related to an increasing age (OR: 0.96/age), and professional sun exposure (OR: 0.5). Intermittent, recreational sun exposure is mainly associated with the prevalence of atypical nevi in our sample and this effect does not depend on skin phototype. Promotion of sun protection, especially in patients with high numbers of common nevi, might serve as a measure to prevent the development of atypical nevi.

Various cytokines are involved in growth regulation of human melanoma cells. Malignant melanoma cells express multiple growth factors, including basic fibroblast growth factor (bFGF), transforming growth factor (TGF)-alpha, platelet-derived growth factor (PDGF)-alpha, and melanoma growth stimulatory activity (MGSA), substances which are not expressed in normal human melanocytes. The simultaneous synthesis of growth factors and expression of their receptors by melanoma cells, leading to permanent stimulation of cell proliferation, has been clearly shown for bFGF and MGSA. This phenomenon has been designated autocrine growth stimulation. Increased or altered expression of growth factor receptors has been described for nerve growth factor (NGF) receptor, for PDGF-beta receptor and for a truncated form of epidermal growth factor (EGF) receptor encoded by the c-erb-B2 oncogene. Lymphokines are mainly involved in growth control of melanoma cells. Interferons (IFN)-alpha, -beta and -gamma, Interleukins (IL)-1 and -6 as well as tumour necrosis factor (TNF)-alpha inhibited melanoma cell proliferation, with the strongest effects displayed by IFN. TGF-beta which was found to inhibit proliferation of normal human melanocytes exhibited marginal effects on melanoma cells, or even stimulated their growth. In conclusion, a complex network of cytokines is involved in the regulation of melanoma cell growth. Further insight into these mechanisms may contribute to the finding of new strategies in melanoma therapy.

In order to enable a direct comparison of gene expression in human melanoma cells and in normal human melanocytes, culture conditions were investigated under which both cell populations can be grown in vitro. Five of 13 melanoma cell lines tested could be cultured to confluence in a melanocyte medium containing fetal calf serum, 12-O-tetradecanoylphorbol-13-acetate and stimulators of cyclic adenosine monophosphate, whereas none could be grown to confluence in a serum-free hormone-supplemented melanocyte medium containing basic fibroblast growth factor and other mitogens. In both melanocyte media the melanoma cells showed signs of increased morphological differentiation with dendrite formation. Normal human melanocytes could be grown in melanoma cell medium for a few days, after which the cultured cells showed a less differentiated phenotype. Since morphological changes may reflect variations in gene expression, we suggest that comparative studies on gene expression of benign and malignant melanocytes should also include thorough investigation under identical culture conditions.

A simple, rapid and reproducible assay for the determination of melanoma cell proliferation in vitro is described, based on the hydrolysis of a fluorogenic substrate by cell esterases in the cytoplasm of living cells. Human melanoma cells were cultured at several densities in 96-well culture plates for 24 h and were then incubated with 4-methylumbelliferyl heptanoate. The generated fluorescence showed a strong correlation with the cell numbers, similar to those assessed by determining the [3H]thymidine incorporation into cellular DNA and by quantifying the fluorescence obtained after DNA labelling with Hoechst 33258. The latter, however, was less sensitive and exhibited higher standard deviations. In addition, the method reliably detected the anti-proliferative effects of the anti-cancer compounds cisplatin and vindesine. It is, therefore, suggested that the fluorometric assay with 4-methylumbelliferyl heptanoate as substrate could prove useful for the screening of potential anti-cancer agents with anti-proliferative activity.