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Melanoma and congenital melanocytic nevi

Systematic review
Results
Comment

Large congenital melanocytic nevi in children are thought to be associated with increased risk of malignant melanoma. Both risk and aesthetic considerations support surgical removal and reconstruction. A systematic review [1] estimates the size of the risk.

Systematic review

The review used two electronic databases to identify English language papers related to large melanocytic nevi in humans up to 2002, and searched other bibliographies. A wide range of descriptions for nevi was used to ensure that all studies were captured. For inclusion studies needed an explicit definition for large congenital melanocytic nevi, and to enrol patients without melanoma. Any that used a definition of greater than 2% of body surface area, or which used nevi more than 20 cm at largest diameter or expected to reach this size were included. The smallest allowable sample was five patients.

Results

Eight cohorts were included, with 432 children (Figure 1). The mean age at entry (when given) was two weeks to 8.4 years, and mean follow up of between 0.7 and 10.5 years. Five studies were prospective and three retrospective. There were more female (57%) than male (43%) children.



Figure 1: Studies of prevalence of malignant melanoma in congenital melanocytic nevi (dark circles were retrospective studies)





Twelve children (2.8%) developed cutaneous malignant melanoma. This incidence was calculated as 2,600 times higher than a similar age group in the general population. In the ten cases where the information was available, the melanoma originated in the large congenital melanocytic nevus.

Of the 432 children, 31 (7%) underwent complete excision, 98 (23%) partial excision, 70 (16%) complete or partial excision, 21 (5%) dermabrasion, 17 (4%) chemical peel, and 194 (45%) were observed.

Comment

Making a decision about treating a child with a large congenital melanocytic lesion is difficult. On the one hand complete excision is not always possible, and if it is possible it can be difficult, with poor cosmetic results. On the other hand the risk of malignant melanoma was thought to be high. This study tells us that melanoma occurs about 3,000 times more frequently in these children than in children without these nevi, and that over an average of about six years one child in 36 will develop malignant melanoma.

Many imponderables remain. This thoughtful systematic review not only gives a useful start, but provides guidance about information to be collected and reported in future.

Reference:

  1. AJ Watt et al. Risk of melanoma arising in large congenital melanocytic nevi: systematic review. Plastic and Reconstructive Surgery 2004 113: 1968-1974.

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