Changes observed in slow-growing melanomas during long-term dermoscopic monitoring

Background: Melanomas vary in growth rate from rapidly developing nodular melanomas to slow-growing melanomas (SGM) that hardly change over years. Objectives: To evaluate longitudinal changes in dermoscopic findings of SGM. Methods We retrospectively analysed a dermoscopic image dataset from 15 pigmented lesion clinics, of SGM that were followed sequentially by digital dermoscopy for at least 1 year. We evaluated baseline and follow-up images for changes in global pattern, organization, colours, structure and size. Results: Our series consisted of 92 SGM. On follow-up, these melanomas developed the following dermoscopic findings: more homogeneous and less reticular global dermoscopic pattern; more frequent disorganization of pattern (baseline, 67% vs. follow-up, 79%); decreased prominence of light brown colour, increased prominence of dark brown colour, and increased frequency of the colours red, white, grey, blue and black (baseline: 29%, 3%, 18%, 6% and 33% vs. follow-up: 41%, 10%, 31%, 13% and 45%, respectively); decrease in prominence of dermoscopic structure of pigmented network, with a concomitant increase in prominence of structureless areas; and increased prominence or new appearance of melanoma-specific dermoscopic structures, including negative network, blue-white structures and blotches. The majority of lesions (75%) remained the same size or grew by < 2 mm in diameter. An increase in lesion size was associated with change in the total number of colours and structures (χ ² = 14·3, P = 0·027) at follow-up. Conclusions: While their diameter changed minimally over time, most SGM became more disorganized, revealed loss of network in favour of structureless areas, and developed new colours.