Causes
Cancer is caused by mutations of the DNA in the nucleus of a cell. The
mutated genes instruct the cell to divide and keep dividing, producing an uncontrolled
growth of cells with the same mutation. We don't understand the process fully,
but we know of many carcinogens, substances that provoke or increase your chance
of getting cancer.
In skin cancer, the primary carcinogen is sunlight. Studies have shown
that melanoma is more common in people who have spent a lot of time in the sun.
The damage caused by ultraviolet (UV) light can lead to mutations. The incidence
of melanoma is rising, a reflection of the boom in sunbathing since the Second
World War.
People of African descent are less likely to get melanoma than Caucasians,
though they can get a rare form which appears on mucus membranes such as the
anus and the inside of the mouth. Among Caucasians, paler people are more susceptible.
The risk goes up with for those with blue or green eyes, fair hair, and freckles.
Most people get the bulk of their sun exposure as children, and people who
had severe sunburn before age 18 are at higher risk of skin cancer. As well
as UV light from the sun or a sunlamp, x-rays have been associated with a risk
for melanoma, as have exposure to radium or arsenic.
Skin cells called melanocytes provide the brown pigment that results
when we tan in the sun. Melanoma always starts in one of these cells. It can
take root in existing moles on the skin, which are actually groups of melanocytes.
On the other hand, melanoma can arise in lone melanocytes in normal skin.
Some moles are more risky than others. Dysplastic nevi are moles
that are abnormal in some way and imply a small possibility of future melanoma.
The way to recognize dysplastic nevi is as simple as ABCDE - they will have
one or more of the following qualities:
- Asymmetry - the mole is not round like normal moles, but is oddly-shaped
or elongated
- Border - the border is irregular, like a rugged coastline on a map,
and the edges fade into the skin rather than making a sharp line
- Color - the mole has areas of different color, possibly including
white, blue, red, or (especially) black
- Diameter - it's larger than the size of a pencil eraser
- Elevation - it's raised above the surface of the skin
Some families have a history of these types of moles. They are at higher risk
of melanoma. How much higher depends on the size and frequency of the abnormal
moles and whether people in the family have previously had melanoma.
Moles like this sometimes change during pregnancy. Usually it means nothing,
but the rate of melanoma is higher in pregnant women.