Currently the neuroectodermal theory of tissular genesis of skin melanoma is most widely recognized. The tumor consists of melanocytes or of nevus cells situated in the basal layer of the epidermis along the dermoepidermal interface. Their main function is synthesis of the melanin pigment, which is taken up and accumulated by epidermal cells.

It is accepted to distinguish three main types of skin melanoma: superficial spreading, nodular and acral-lentiginous melanomas. Two phases are distinguished in melanoma: the horizontal phase, when the disease spreads within the epithelial stratum, and the vertical phase, when malignant cells penetrate into superficial layers of the epidermis with invasion of the basal membrane of the derma and hypodermic fatty tissue. The horizontal phase of superficial spreading melanoma lasts for up to 7 years, while that of acral-lentiginous melanoma lasts for 10–20 years. The vertical phase as a rule is characterized by rapid tumor growth and tendency to metastasis.

In 60% of cases it is superficial spreading melanoma that is observed. Initially it looks like a black or brown pigment spot with diameter no larger than 0.5 cm that does not rise over skin surface. In the vertical phase, heavy tumor growth with formation of an exophytic component takes place. Nodular melanoma is observed approximately in 20% of cases, it is in the form of a node, fungus or polyp of a black or blue-red color. Acral-lentiginous melanoma accompanies Dubrey’s melanosis and constitutes 20% of all skin melanomas. The horizontal phase of pathological formation is long and transition of lentigo to lentiginous melanoma occurs gradually. During malignant transformation, a lentigo acquires an irregular form with scalloped contours and uneven pigment distribution.

Melanomas metastasize by the lymphogenic route to skin and lymph nodes, and by the hematogenic route to the liver, lungs, brain, bones, kidneys and adrenal glands. The tendencies of the tumor process disseminating depend upon the biological characteristics of a given pathological formation. Some forms are observed which metastasize for a long time only lymphogenically to regional lymph nodes. At the same time, there are melanomas with high malignancy potential, with a tendency to early hematogenic dissemination. Forms of melanomas which metastasize to the skin should be particularly stressed. Among them there are satellite, nodular, erysipeloid and thrombophlebitis-like forms. Satellites are multiple small eruptions situated near the primary focus or at some distance from it in the form of spots retaining the color of the tumor. The nodular form of skin metastases manifests itself as multiple subcutaneous nodes of different size, which may be situated at any distance from the primary formation. The erysipeloid form of skin metastases looks like an area of bluish-red edematous skin surrounding the tumor. The thrombophlebitis-like melanoma manifests itself by radial spreading, painful hardening, enlarged superficial veins and skin hyperaemia around the tumor (Vazhenin et al. 2003).

Diagnosing skin melanoma presents some difficulty. At the beginning of the disease there is no distinct clinical picture, and consequently tumor is hard to distinguish from benign pigment formations. In diagnosing skin melanoma, data of visual examination, palpation, and radioisotopic, thermometrical and morphological methods of examinations are used.

When visually examining a cutaneous covering, it is preferable to use a magnifying glass. Both the tumor itself and the whole skin surface should be examined in order to exclude primary multiple melanoma. The form, size, colour of the tumor and integrity of the epidermis over it are visually assessed.

The primary tumor, surrounding soft tissues and all the lymph nodes available for examination are subjected to palpation. It is necessary in order to determine tumor consistency and the degree of its displacement relatively to subjacent tissues as well as to detect transient, regional and distant metastases of melanoma. Secondary changes in the skin have even edges, round form and dense elastic consistency. Lymph nodes affected by melanoma metastases are enlarged and assume a dense consistency.

Radioisotopic examination is done with twice-substituted sodium phosphate labeled with radioactive phosphorus. The substance is introduced orally on an empty stomach and then radiopharmaceutical (RP) uptake into the tumor and that in the symmetric area of healthy skin are compared by way of contact radiometry. According to some data, RP hyperfixation over a melanoma is four-times as high as that over the contralateral intact area of the epidermis.