Melanoma

Melanoma is an invasive malignant tumour of melanocytes. Most cases occur in white adults over the age of 30, with a predominance in women.

Incidence

The incidence of melanoma has doubled over the past 10 years in Australia (currently 40/100 000 population) and shown a similar increase in other countries. In Europe twice as many women as men develop melanoma—about 12/100 000 women and 6/100 000 men.

Prognosis

The prognosis is related to the thickness of the lesion, measured histologically in millimetres from the granular layer to the deepest level of invasion. Lesions less than 0-76 mm thick have a 100% survival at five years, 0-76-1-5 mm thick an 80% survival at five years, and lesions over 3-5 mm less than 40% survival. These figures are based on patients in whom the original lesion had been completely excised. A recent study in Scotland has shown an overall five year survival of 71-6-77-6% for women and 58-7% for men.

Sun exposure

The highest incidence of melanoma occurs in countries with the most sunshine throughout the year. However, skin type and the regularity of exposure to sun are also important. The incidence is much greater in fair skinned people from higher latitudes who have concentrated exposure to sun during holidays than in those with darker complexions who have more regular exposure throughout the year. Severe sunburn may also predispose to melanoma.

Genetic factors

Since melanin protects the skin from ultraviolet light it is not surprising that melanoma occurs most commonly in fair skinned people who show little tanning on exposure to sun, particularly those of Celtic origin. Members of families with the dysplastic naevus syndrome are more likely to develop melanoma in their moles. These patients have multiple naevi from a young age.

Pre-existing moles

It is rare for ordinary moles to become malignant but congenital naevi and multiple dysplastic naevi are more likely to develop into malignant melanoma.

Congenital hairy naevus Dysplastic naevus syndrome

Nodule developing in superficial spreading melanoma
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