Melanoma is the most serious type of skin cancer. It starts when the pigment-producing cells in your skin (melanocytes) become abnormal and grow out of control.

Melanoma usually looks like a flat, brown or black mole that has irregular, uneven borders. Most melanomas show up as a new spot or skin growth. But they can form in an existing mole or other mark on the skin. Less often, melanoma begins in other places, such as under the nails, in the eye, or in the intestines.

Treatment works best when melanoma is found early.