Background: Recent evidence suggests that melanoma is a family of different tumours with varying abilities to grow and metastasize. Trends in melanoma epidemiology show a strong increase in the incidence of thin melanoma, with no corresponding increase in mortality or incidence of thick melanoma. We initially evaluated five cases and found that none had baseline features suggestive of melanoma; excision was performed based on slight changes visible only in side-by-side comparisons of dermoscopic images.
Objectives: To assess the clinico-dermoscopic features and the growth patterns of melanomas that were excised after a follow-up of 1 year or more due to their inconspicuous features at the baseline consultation.
Methods: In a multicentre, retrospective study of histopathologically confirmed melanomas excised after follow-up, we analysed dermoscopic images obtained at the initial consultation and compared them with images obtained at the last follow-up consultation. Images were analysed and graded using standard algorithms and scored for changes in size, symmetrical or asymmetrical structural change, and development of new melanoma-specific criteria. An overall score reflecting the amount of change was calculated for each lesion.
Results: Our series consisted of 103 melanomas. After a median follow-up of 20 months, most lesions were still in situ or early invasive (median Breslow thickness of 0.48 mm), with only three lesions showing tumour thickness of 1 mm or more. The most frequent baseline characteristics were asymmetrical pigmentation (78.6% of lesions), reticular overall pattern (62.1%), and regression features (35.9%). Most melanomas (58.3%) showed minor to moderate changes over time, with < 2 mm size increase, with asymmetrical structural change, and without development of new melanoma-specific criteria. Major changes were visible only after a mean follow-up of 33 months.
Conclusions: This study provides evidence for the existence of a subgroup of slow-growing melanomas, which may explain the increase in the incidence of thin melanoma, despite stable rates of thick melanoma and melanoma-associated mortality.