Melanoma is a cancer of the cells that give skin its color. It is the skin cancer most likely to spread, and it is also one of the most curable cancers when it is found early.
Melanocytes are the cells that make melanin, the pigment that colors skin, hair, and eyes. They sit at the bottom of the epidermis, the thin top layer of the skin. When the DNA in a melanocyte is damaged, most often by ultraviolet (UV) light, the cell can start to divide without control. That growth is melanoma.1
About 7 in 10 melanomas appear as a new spot on skin that looked normal, according to a pooled analysis of 38 studies. The rest grow inside a mole that was already there.2 Melanocytes also live in the eye, under the nails, and in the moist linings of the mouth, nose, and genitals, so melanoma can start in those places too.
A melanoma that is still confined to the skin is usually cured with an operation done under local anesthesia. About 77% of melanomas in the United States are found at this localized stage, and 5-year relative survival for that group is above 99%.3 Once melanoma reaches nearby lymph nodes the figure is 76%, and after it spreads to distant organs it is 34%.3
Those numbers describe large groups of patients diagnosed between 2016 and 2022. They can't predict the course for one person, and treatment for advanced melanoma has improved quickly over the past decade.
For a melanoma that has not spread, the most important finding is its thickness in millimeters, called Breslow depth. A pathologist measures it under the microscope. Thickness, together with ulceration (a breakdown of the skin over the tumor), sets the tumor category in the staging system doctors use worldwide.5
ABCDE, the ugly duckling sign, and what happens after you point a spot out.
Risk factors ranked by strength, and the ones you can change.
Stages 0 through IV in plain language.
Reviewed against these sources in September 2026. Figures change every year, and this page is updated when new estimates are released.
