A deadly skin cancer. It develops in pigment-producing cells, most commonly on the upper back, trunk, head, neck, and lower legs. While the cure rate is high when caught early, unchecked cases can spread to internal organs. Malignant moles tend to have asymmetrical or irregular borders, uneven color, a diameter greater than six millimeters, and/or a rapidly changing appearance. While genetics and immune disorders increase risk, a history of sun- or tanning-bed exposure is the most preventable cause.