Cutaneous melanoma of the haired skin arises from melanocytes in the skin's outer layers. Unlike oral melanoma, the majority (over 80%) of melanocytic skin tumours on haired skin are benign growths called melanocytomas. These benign tumours are typically small, dark, well-circumscribed lumps that are cured by simple surgical removal. A minority are truly malignant melanomas, and even these tend to behave less aggressively than oral melanomas, though a subset can metastasise. Determining whether a given melanocytic skin tumour is benign or malignant requires histopathological examination — the microscopic features including the mitotic index (how rapidly cells are dividing) and Ki-67 proliferation marker help predict behaviour. Miniature Schnauzers, Scottish Terriers, and Vizslas are among the breeds more commonly affected.