Causes of melanoma

Repetitive scorching burning by sunshine/ultraviolet (and interestingly it may be intermittent high doses that are more predisposing than chronic exposure c.f. other skin cancers), particularly when suffered by fair skinned individuals in youth, is a predisposing factor for the development of melanoma and this explains why the disease is more common in Caucasian races living nearer the equator, and the lower incidences in black races. There are some data that suggest that ultraviolet dependent melanoma has a slightly better prognosis than other types.

 

From the above, it has been established that excessive exposure of the Caucasian skin to ultraviolet radiation (mainly in the form of natural sunlight)is the main environmental risk factor for causing/triggering malignant melanoma. What has not yet been established is the exact wavelength or wavelengths that are most effective at triggering this malignant change in melanocytes. Studies from Western Canada and other regions of the world strongly suggest that intermittent burning exposure of unacclimatised Caucasian skin is a major risk factor for the development of melanoma.

 

Other predisposing factors are the dysplastic naevus syndrome – a familial condition of multiple congenital dysplastic naevi (‘moles’) and the cancer predisposition syndrome: the Li Fraumeni syndrome, that runs heavily in families and runs to multiple other primary cancers. Of course, many cases arise in patients with no obvious predisposing cause.

 

Thus far, three genes have been identified which influence malignant melanoma risk. These are: the CDKN2A gene on chromosome 9 , the CDK4 gene on chromosome 12 and a gene on chromoosome 1. The first of these : CDKN2A gene is mutated in 20-30% of faamilies with melanomaa and is recognised as an important gene controlling entry into cell mitotic cycle.