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Objective: Cutaneous melanoma represents the most frequent skin tumor in horses. Even though epidemiological and clinical pathological features have been examined in detail and immunological and molecular biological studies of equine melanoma have been carried out, its pathological mechanism remains unclear. In humans, neovascularization of melanoma corresponds to prognosis, and vascular mimicry has been described for different types of human melanoma. In order to investigate neovascularization, objective of this study was to establish an in vitro model of equine melanoma.
Materials and methods: Samples from the perineal region of two grey geldings were obtained to establish melanoma cells in vitro. Immuno-cytological staining was performed using antibodies to anti-S100, anti-MAGE, anti-MITF, and anti-TYRP1 as melanocytic markers. Moreover, semi-thin sections were prepared for transmission electron microscopy to investigate their ultrastructure with regard to marker organelles, i. e. melanosomes, which are tissue-specific lysosome-related organelles of pigment cells.
Results: Two populations of cells could be cultivated. One type of cell closely resembled keratinocytes when compared to semi-thin sections of melanoma. Monolayers of these cells consisted of epithelioid type cells similar to cells forming the tumor in vivo. The other type of cells displayed dendritic protrusions and stained positive for all melanocytic markers. These cells proliferated and started forming nodular formations after 13 days. In histological cross-sections of these nodules tubular structures were visible. Transmission electron microscopy confirmed the presence of melanosomes as marker organelles for melanocytes.
Conclusion and perspective: The cultivation of equine melanoma cells resulted in the successful establishment of an in vitro model of the tumor, with macroscopical and microscopical characteristics similar to the in vivo situation. Further studies are aimed at investigating the vessel-like tubular structures with regard to angiogenic properties and/ or vascular mimicry.