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Malignant melanoma is considered the most aggressive form of skin cancer. The incidence rate of the disease has steadily risen over the past few decades throughout the world. If melanoma is diagnosed early, it can be cured by surgical resection, but as soon as the first distant metastasis appears, the disease becomes one of the most aggressive types of metastatic, chemoresistant lesions. Cutaneous melanocytes originate from highly motile neural crest progenitors that migrate to the skin during embryonic development. They are pigment-producing skin cells that reside between keratinocytes in the basal layer of the epidermis, producing melanin in response to a variety of external stimuli, such as ultraviolet (UV) radiation. Although UV radiation is the main exogenous etiological risk factor for the development of the disease, other presently unknown factors are also involved. As estimated by the World Health Organization worldwide number of newly diagnosed skin cancer cases is between 2 and 3 million each year, of which 132,000 are melanoma. Additionally, in most western countries, the incidence of melanoma doubles roughly every decade. Malignant melanoma progresses through a series of well-defined clinical and histopathological stages, advancing in a stepwise manner from either a common acquired or a dysplastic nevus through the primary radial growth phase (RGP) and the vertical growth phase (VGP) to distant metastasis [Welch et al., 1997]. Different subtypes of the disease represent diverse entities, as there are marked differences in their biological behaviours. While the most common superficial spreading subtype (SSM) is characterised by a prolonged RGP, nodular melanoma (NM) begins to grow vertically from its onset. Clinical staging of primary cutaneous melanoma is based on measurements of tumour thickness (in millimetres), the presence or absence of ulceration, penetration through cutaneous layers, mitotic rate and evidence of lymph node, cutaneous or distant metastasis [Chin et al., 2006]. The vertical progression of lesions is representative of the degree of tumour progression and is measured by the Breslow thickness, which was first used in the early 1970s and measures the thickness of the tumour from the top of the epidermal granular layer (or from the ulcer base if the tumour is ulcerated) to the innermost depth of invasion. Ulceration of the tumour surface of melanoma covering the epidermis is one of the most sensitive parameters of metastatic potential. The currently used diagnostic and prognostic approaches to recognise |
