Melanoma also known as malignant melanoma, is a type of cancer that develops from the pigment-containing cells known as melanocytes. It is the most dangerous form of skin cancer. It is caused mainly by intense, occasional UV exposure (frequently leading to sunburn), especially in those who are genetically predisposed to the disease. Melanomas often resemble moles; some develop from moles. Early signs of melanoma are changes to the shape or color of existing moles. The majority of melanomas are black or brown, but they can also be skin-colored, pink, red, purple, blue or white. They typically occur in the skin but may rarely occur in the mouth, intestines, or eye. In women they most commonly occur on the legs, while in men they are most common on the back. Diagnosis is confirmed by a skin biopsy of any concerning skin lesion. Avoiding UV light and the use of sunscreen may prevent melanoma. Treatment is typically removal by surgery. In those with slightly larger cancers, nearby lymph nodes may be tested for spread. Most people are cured if spread has not occurred. In those in whom melanoma has spread, immunotherapy, biologic therapy, radiation therapy, or chemotherapy may improve survival.