SOLAR KERATOSES - A RISK FACTOR FOR MELANOMA BUT NEGATIVE ASSOCIATIONWITH MELANOCYTIC NEVI

Solar keratoses have been associated with increased risk of squamous-c ell and basal cell carcinomas, but their association with melanoma is less clear. This study investigated solar keratoses as a risk factor f or cutaneous melanoma in Australia, also associations between solar ke ratoses and other host factors associated with melanoma. A total-body naevus count was made of 258 melanoma cases and 281 controls recruited from New South Wales, Australia, and solar keratoses were counted on the left forearm. Solar elastosis was also assessed by clinical examin ation on the face and the side of the neck. Solar keratoses were a sig nificant risk factor for melanoma in Australia. The presence of IO or more solar keratoses on the left forearm (compared with none) was asso ciated with an odds ratio of 4.7 (95% CI, 2.0-10.9). A highly signific ant association was found between number of solar keratoses and a past history of multiple basal-cell carcinomas in cases and controls respe ctively. Numbers of common and atypical naevi decreased significantly with age, while solar keratoses wore more common in older individuals. Solar keratoses were found more commonly in men than women in cases a nd in controls ( p < 0.0001), A negative association was found between numbers of common naevi and numbers of solar keratoses in cases and c ontrols, and this remained significant after stratifying for age, gend er and hair colour (p < 0.0001 and p < 0.0016 respectively). Solar ker atoses were more common in males with melanoma on the head and neck as compared with melanoma on any other site. Solar keratoses and naevi w ere independently predictive of increased melanoma risk. The fact that these 2 phenotypes were found to be negatively associated suggests th at susceptibility to melanoma may be expressed via 2 distinct cutaneou s phenotypes which may be genetically determined. Int. J. Cancer 78:8- 12, 1998. (C) 1998 Wiley-Liss, Inc.