Melanoma is a unique type of cancer arising from the melanocyte cell lineage, which is the pigment forming cell of the skin and mucosa. As has been said above, the incidence of melanoma in Europe is rising but, interestingly, the death rate from this disease is falling. This improved prognosis is almost certainly due to earlier diagnosis in a more 'aware'/health conscious population. In 1984 Clarke promulgated his notion of a melanoma's growth pattern and progression: In the first instaance, many melanomas undergo a 'radial' phase of horizontal growth within the epidermis (the most superficial layer of the skin). At this stage the disease is relatively 'low risk' as the malignant cells within the epidermis do not have access to the lymphatics or blood vessels which provide routes of dissmination (metastaasis). Thereafter, at a time which varies between individual tumours, there follows a phase of downward or 'vertical' growth into the dermis and beyond - at this time the melanoma acquires a solid or nodular feel to it. At this later time, the disease becomes a much more potentially dangerous condition as the routes of dissemination - viz. blood and lymphatic - (metastatic spread) are opened up to the malignant cells and there is no doubt that melanoma has a predilection to travel elsewhere in the body if access to these vessels is available.
From the foregoing, it can be appreciated that the superficial spreading or radial phase melanoma has a good outlook/prognosis and a nodular or vertically growing melanoma a much more uncertain prognosis. A variant of the superficial spreading melanoma is the lentigo maligna melanoma which is a melanoma variant that occurs on the faces of the elderly, who have been chronically exposed to sunlight. It is confined to the epidermis and has a good outlook if resected as it has not penetrated deep. Aanother way of prognosticating about the depth of invasion within the skin layers and hence of assessing a patient's risk is by using the Breslow thickness scale. In 1970, Breslow introduced the method of measuring the thickness of a melanoma as method of microstaging and prognosticating. He identified a group of patients with melanomas less than 0.76 mm thick that seldom metasised after resection. Those whose melanomas were 0.77-4.0 mm thick represented an intermediate group of patients with regard to prognosis (this intermediate group subsequently broken down into low-intermediate risk: 0.76-1.5 mm and high-intermediate risk : 1.6-4.0 mm thickness ) and high risk patients whose melanoma thickness was greater than 4.0 mm. Breslow's measurement of thickness became the most widely accepted measure of future prognosis (relapse risk and survival chance).
