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Bitesize evidence: Melanoma risk 0.7 per cent in melanocytic naevi

Q. What is the risk that a congenital melanocytic naevus will undergo malignant transformation?

SynopsisCongenital melanocytic naevi are pigmented lesions of varying size that are present at or shortly after birth. They occur in between 0.2 per cent and 2.1 per cent of infants, and range in size from less than 1cm2 to hundreds of cm2. Previous case series and cohort studies have provided varying estimates of the risk of malignant transformation. This systematic review identified 14 relevant articles after a comprehensive literature search. Studies with fewer than 20 patients or those with fewer than three years of follow-up were appropriately excluded. Eight studies were retrospective and six were prospective, and the mean follow-up ranged from 3.4 to nearly 24 years. Six studies had fewer than 100 patients; two studies were quite large, with 1,008 and 3,922 patients. The proportion of patients with melanoma ranged from 0 per cent to 10.7 per cent (six out of 56 patients in one small retrospective study). The age at diagnosis of melanoma ranged from birth to 57 years, with a mean age of 15 years. Overall, 49 melanomas were reported in 46 of 6,571 patients (0.7 per cent). Most (75 per cent) arose in so-called 'garment naevi', which are bigger than 40cm in diameter. Because of the higher rate in small studies, suggesting selection bias, this figure of 0.7 per cent probably represents an upper bound. The largest and perhaps best population-based study found that 0.2 per cent of all newborns were registered as having CMN, of whom only two (0.05 per cent) underwent malignant transformation after a median follow-up of 10 years. Level of evidence2a (see www.infopoems.com/levels.html)

Reference
Krengel S et al. Melanoma risk in congenital melanocytic naevi: a systematic review. Br J Dermatol 2006;155:1-8

Bottom line

Less than 1 per cent of congenital melanocytic naevi reported in the medical literature underwent malignant transformation, although the heterogeneous nature of the studies permits only a broad estimate of risk. The true rate of malignant transformation may be lower because of selection bias inherent in smaller studies.

This Patient Oriented Evidence that Matters (POEMs) is taken from InfoPOEMS/ Inforetriever, a point of care evidence-based medicine tool, published by John Wiley. For more information, e-mail: freynold@wiley.co.uk or visit www.infopoems.com

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