Definition: Melanoma is the most serious type of skin cancer. It occurs when skin cells called melanocytes are exposed to ultraviolet (UV) radiation. If the skin receives too much ultraviolet light, the melanocytes may begin to grow abnormally and become cancerous. 
Melanocytes are the cells that make melanin, which gives skin its color.  Melanin also protects the deeper layers of the skin from the sun's harmful ultraviolet (UV) rays.
Melanoma occurs when something goes wrong in the melanocytes that give color to your skin. Normally, skin cells develop in a controlled and orderly way — healthy new cells push older cells toward your skin's surface, where they die and eventually are sloughed off. This process is controlled by DNA. But when DNA is damaged, new cells may begin to grow out of control and can eventually form a mass of cancerous cells. 
Just what damages DNA in skin cells and how this leads to melanoma is a matter of intense study. Cancer is a complex disease that often results from a combination of factors, including environmental and genetic factors. Still, excessive exposure to ultraviolet (UV) radiation is a leading factor in the development of melanoma. This can be radiation is from the sun or from tanning lamps and beds. However, UV light doesn't cause all melanomas. 
1. Fair skin Having less pigment (melanin) in your skin means you have less protection from damaging UV radiation. If you have blond or red hair, light-colored eyes, and you freckle or sunburn easily, you're more likely to develop melanoma than is someone with a darker complexion.  However, melanoma can develop in people with darker complexions, including Hispanics and blacks. For these people, melanoma is often diagnosed in the more dangerous later stages. 
2. A history of sunburn. Every time you burn your skin, you increase your risk of developing skin cancer. People who have had one or more severe, blistering sunburns as a child or teenager are at increased risk of skin cancer as an adult. Although sunburns in adulthood also are a risk factor, the greatest damage seems to occur before you're 18. Infants are particularly vulnerable because the melanin in their skin isn't yet fully developed. 
Signs and Symptoms
The first sign of melanoma is often a change in the size, shape, or color of a mole. But melanoma can also appear on the body as a new mole.  Abnormal moles can appear anywhere on the skin. That's why it is important to always examine your skin to check for new moles or changes in moles.
In men, melanoma most often shows up:
In women, melanoma often develops on the lower legs.
If you notice any of the following on your skin, see your doctor as soon as possible for a screening check.
It is important to find melanoma as early as possible. The American Cancer Society recommends a skin examination during a routine cancer-related check-up in all adults age 20 years and older. 
There are two kinds of biopsies that are performed to diagnose melanoma: excisional biopsy and sentinel lymph node (SLN) biopsy. An excisional biopsy is done to find out whether a mole is actually melanoma. An SLN biopsy is done after melanoma is diagnosed, to find out whether the cancer has spread beyond the skin. 
Stages of Melanoma
Melanoma is staged using the numbers 0 through IV. Stage 0 melanoma is also called in situ melanoma.  At this stage, the cancer is confined to the epidermis and hasn't begun to spread. Treatment consists of complete surgical removal only. 
Stages I through IV cancers are invasive tumors that have the ability to spread to other areas. A stage I cancer is small and well localized and has a very successful treatment rate through surgical removal. The higher the stage number, the lower the chances of a full recovery. By stage IV, the cancer has spread beyond your skin to other organs, such as your lungs, liver and bone. Although it may not be possible to eliminate the cancer at this stage, treatment with radiation or biological or experimental therapies may help alleviate signs and symptoms. 
The best treatment for early-stage melanomas is surgical removal. Very thin melanomas may have been entirely removed during the biopsy and require no further treatment. Otherwise, a surgeon will excise the cancer as well as a small border of normal skin and a layer of tissue beneath the skin. In almost every case this eliminates the cancer. 
Treating melanomas that have spread beyond the skin
If melanoma has spread beyond the skin, treatment options may include :
Clinical trials for treatment of melanoma are ongoing. Ask your physician if you would like to participate in a clinical trial.