Melanomas that arise in pre-existing moles may initially alter the pigment network within the central area and spare the borders.
Over a three-month period, a 45-year-old woman noted progressive darkening of a longstanding mole, measuring 6 mm in diameter, on the dorsum of her right foot (Figure 1). Dermoscopy showed an asymmetrical mole with an irregular pigment network with regional variation in intensity. A darkly pigmented branched component with globules and dots was in the centre of the mole (Figure 2). Excision biopsy showed nests of atypical melanocytes within the epidermis and upper dermis, which were obscured by a marked lymphocytic reaction. The surface of the skin had collections of red cells, melanocytes and melanin pigment between keratin filaments (Figure 3).