What is it?
Melanoma is a malignant tumor developed from melanocytes.
Melanocytes are found in the skin, mucous membranes, eyes and central nervous system. This is one of the most aggressive cancers that are, but the treatment at an early stage helps to heal the patient.
Epidemiology
The incidence of melanoma is increasing rapidly for several years.
This is one of the most common cancers in young adults and those whose frequency increases most in the world.
For 40 years, the number of melanoma is doubling every 5 years, the other skin cancer every 10 years.
Melanoma the most deadly today that only 5% of skin cancers, but their impact is growing concern.
The incidence of malignant melanoma in France of 3.45 new cases per 100 000 among men and 6.58 among women, with 3,000 to 4,500 new cases per year.
Causes and risk factors
Are the following:
* The sudden exposure of skins in the sun during childhood;
* The existence of numerous pre-existing pigmented nevi.
The role of phototype is known. Individuals to clear phototype are the most threatened. Eyes or blue, hair blond or red, the complexion clear, the presence of Ephelides (freckles), the tendency to sunburn, the inability to tan are significant risk factors for melanoma (multiplied by 2 or 3). The sun burns received in childhood and adolescence doubled the risk of subsequent occurrence of melanoma. Genetic factors seem to determine the cytological susceptibility to carcinogenic effect of ultraviolet rays. The importance of phototype is demonstrated by the exceptional nature of malignant melanoma among blacks.
The intermittent exposure, brutal, intense and repeated the combination of these exposures are factors equally important and more significant than the cumulative exposure over a lifetime.
Exposure to lamps UV-room or home increases the risk of developing melanoma by three if phototypes clear. Indeed, the exhibition gives high levels of UV rays on a short time, for intermittent periods on skin not normally exposed.
Most malignant melanomas develop from melanocytes in the skin, there are only 20 to 40% arising from a pigmented nevus. This means all qu’enlever moles of a patient does not guard against the occurrence of melanoma.
The problem of congenital naevi present at birth, remains unresolved. The congenital naevi are small in 1% of cases. Very large nevi are very rare (1 / 20500).
Nothing is known about the development of small and medium congenital naevi.
For large (over 20 cm): the risk of cancer would be 5 to 20%.
The number of naevi (diameter greater than 5 mm) is against a marker because it is the primary risk factor for the simplest and most decisive although these nevi are not precursors of melanoma mandatory.
The presence of dysplastic naevi was identified as an important précuseur melanoma in the context of familial melanoma.
The degeneration of a nevus is rare: 1 / 700 000. Nevertheless the suspect if the naevus:
* A changed color, became polychromed with extension of the pigmentation on the skin;
* A grossi stood, was covered with scales or crust;
* Ulcerate, bleed or itch.
A set of the experimental and epidemiological evidence shows that sunlight is an important factor in the formation of melanoma.
The highest incidence of melanoma is in Queensland, Australia where it is four times higher than in the USA, itself two times higher than in Canada and three times higher than in the United Kingdom .
Latitude determines the amount of ultraviolet rays. The importance of latitude of residence during childhood determines the risk of melanoma late, which has been confirmed many times for immigrants in the USA, the British settled in Australia, the Europeans settled in Israel.
Other factors play a significant role: the altitude, local topography, cloud cover, fog, suspended particulates, air pollution, reduction of the ozone layer.
Solar explosions are followed by peaks in frequency of melanoma.
The risk of melanoma decreases when the degree of pigmentation increases, in other words, the more the complexion of the skin is clearer, the risk of developing melanoma is high and vice versa. The reduction of the ozone layer resulting from various kinds of pollution could be one explanation for the constant increase in the incidence of malignant melanoma.
The exact mechanisms of carcinogenesis that are poorly known wavelengths in question (particularly UVB but UVA also plays a role) and the stage of carcinogenesis concerned (initiation or promotion) remain to be clarified. UVB occur by several biochemical processes (increase of the-ornithine decarboxylase activity, mutagenic effect of phaeomélanines), immunological (depression of cellular immunity by urocanic acid by the action of oxygenated sterols).
The sun may even act on precursors of melanoma (dysplastic nevi).