High counts of normal melanocytic naevi are a risk factor for cutaneous malignant melanoma

Abstract

We have carried out a case control study on 200 patients presenting in the past 3 years with primary cutaneous malignant melanoma and 200 age‐ and sex‐matched controls. Total body melanocytic naevus counts were performed on all 400 subjects by four trained dermatologists. Analysis was by stratum matched logistic regression, with stratum matching for age, sex and city of treatment. Each variable was adjusted for the other risk factors found in the study, such as hair and eye colour, skin type, amount of UV exposure and episodes of acute sunburn. Substantially increased risk of malignant melanoma was found for persons with large numbers of normal benign melanocytic naevi, with any moles larger than 7 mm in diameter, and also with irregular edges and colour variation in moles—the so‐called dysplastic naevi. The number of moles present on the same anatomical areas as the tumour (arms, legs, trunk, face, head and neck, and palms and soles) was a stronger predictor of melanoma incidence than was the total number of body moles. The relationship of histology and Breslow thickness of melanoma to site, sex, age and number of naevi will also be presented. Our results show that a very high‐risk group for melanoma can now be identified and these patients should be advised about avoiding excessive sun exposure and the early recognition of cutaneous melanoma.