Final congenital melanocytic naevi colour is determined by normal skin colour and unaltered by superficial removal techniques: a longitudinal study

BACKGROUND: Spontaneous lightening of congenital melanocytic naevi (CMN) has not been studied systematically. Final colour is considered an important outcome after superficial removal techniques such as curettage, dermabrasion or laser ablation, and is often compared with colour at birth. OBJECTIVES: To quantify the natural history of CMN lightening over time, and explore phenotypic and genotypic predictors of colour change. METHODS: A longitudinal cohort study was undertaken of 110 patients with CMN (mean follow‐up 5·3 years). Accurate colour‐space measurements were taken from professional serial photographs of CMN and normal skin. Changes in colour over time were modelled using multiple logistic regression, against phenotypic and genotypic variables. RESULTS: Lightening of CMN was significantly associated with lighter normal skin colour (P < 0·001) and with MC1R variant alleles (red/blonde hair gene) (P < 0·001), but not with CMN colour in the first 3 months of life, NRAS genotype or projected adult size of CMN. Importantly, the final colours of adjacent treated and untreated areas of CMN were indistinguishable. CONCLUSIONS: Final CMN colour in childhood is related to the genetically determined skin colour of the individual, is unrelated to the colour of CMN at birth, and is unaffected by superficial removal. What's already known about this topic? Final colour of congenital melanocytic naevi (CMN) is considered an important outcome after superficial removal techniques such as curettage, dermabrasion or laser ablation, and is often compared with colour at birth. The phenomenon of spontaneous lightening in CMN, in which naevi lighten gradually and sometimes dramatically during childhood, has been described but not systematically studied. What does this study add? Final CMN colour in childhood is significantly associated with the individual's normal skin colour, and with MC1R genotype, and is therefore genetically determined. Final CMN colour is not predictable from CMN colour in the first 3 months of life. Superficial removal techniques do not alter the final colour of CMN.