Linked are three references that review some risk factors for melanoma. Please print out these references or review them online.
Some ultraviolet light risk factors have been reviewed under carcinogenesis. Hereditary factors can be important.
Fair skin is obviously an inherited risk factor. Darker skinned Caucasians have a significantly lower risk of developing all types of skin cancer than fair skinned Caucasians, assuming that both have an equal amount of light exposure. South Asian skin appears to be quite protective, as is East Asian and, of course, Black skin. Heredity can also be influential in other ways. In a family of similar skin tones, there can be a dramatically different risk of skin cancer. This seems to relate to a genetic susceptibility, although the exact mechanism is not known. A specific example of this is a tendency towards numerous nevi from a given amount of sun exposure. The absolute number of nevi is the single greatest predictor of melanoma risk on a population basis.
An acquired nevus is the result of a single melanocyte that became abnormal and began to divide. These abnormal melanocytes pile up, causing a brown spot. Most nevi, probably at least 9 out of 10, are secondary to sun damage. Some individuals are far more likely to develop a large number of nevi with a specific amount of ultraviolet light.
Another example of heredity is the tendency towards developing abnormal nevi. This has been called the dysplastic nevus syndrome, or the cancer family multiple mole syndrome, and is manifested by not only an increased number of nevi, but by clinical atypia. The nevi in these individuals seem to be more genetically unstable. There is large variation of colour and edge in these nevi, implying subclones of cells that produce variable amounts of melanin, or grow at different rates. These patients and their families are at particularly high risk for developing melanoma.
The congenital nevus is another risk factor for melanoma. It is well known that large congenital nevi, bigger than 2 palms of one's hand, are at significant risk for developing melanoma over a lifetime. The lifetime risk of a 5 cm diameter hairy congenital nevus may be in the order of 5%, but large prospective series have not been published. Smaller congenital nevi appear to have a smaller risk, proportionate to their size. Less than 2% of the population is born with a single mole. All of the others we acquire, mostly from sun damage.
Congenital nevi can be broadly divided into three types. The first is the most common nevus cell nevus. This is generally manifested as a brown raised lesion that is often hairy. It is the congenital nevus with the most data. Most experts agree that a congenital nevus of this morphology should be surgically removed, if that is practical.
The second type of congenital nevus is the congenital blue nevus. The congenital blue nevus is a blue-black plaque on the skin. There is not good epidemiological data but it appears to be more common in East Asians than in Caucasians. The risk of melanoma arising in such lesions is not well understood, but there is some evidence that the risk is high enough to warrant prophylactic removal of such lesions.
The third type of congenital nevus can be called the hamartomatous type. This is a large lesion, found in neonates, with many histologic patterns in each lesion. The hamartomatous type may show soft tissue sarcoma like changes in areas, as well as melanoma changes in other areas. The hamartomatous congenital nevus appears to be at very high risk for developing multiple cancers, and its early removal is recommended.