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Melanoma is the least common of the 3 main types of skin cancer. Other types are called non-melanoma skin cancers and usually include basal cell and squamous cell carcinomas.
Melanoma occurs when pigment cells in the skin (called melanocytes) mutate and begin growing out of control. This is often related to excessive sun exposure, either from natural sunlight or artificial sources, such as indoor tanning beds. The abnormal cells form a spot or lesion that can be seen on top of the skin. The spot can be entirely new, or less commonly involve a prior mole on the skin.
Many melanomas are diagnosed before they grow into surrounding areas or spread in the body. Others may grow into nearby tissues (mainly regional lymph nodes) or spread to other parts of the body (metastasize).
Melanoma is less common than non-melanoma skin cancer. In general, these skin cancers are highly treatable if they are detected and treated early.