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. Treatment works best when melanoma is found early.