WAIKOLOA, HAWAII — Nevi displaying a specific high-risk pattern on dermoscopy appear to indicate a several-fold greater melanoma risk than is conferred by the presence of clinical dysplastic nevi, Dr. Allan C. Halpern said at the annual Hawaii dermatology seminar sponsored by Skin Disease Education Foundation.
This finding from a recent pilot study that he characterized as “very small, preliminary, but thought provoking” suggests dermoscopy may enable physicians to do a significantly better job of identifying patients at high risk of developing melanoma, said Dr. Halpern, chief of the dermatology service at Memorial Sloan-Kettering Cancer Center, New York, and cochairman of the National Council on Skin Cancer Prevention.
For the past couple of decades, experts have considered the presence of dysplastic nevi to be one of the most potent available markers of increased risk of developing melanoma. Dysplastic nevi are a stronger risk factor than total skin nevus number, which in turn conveys more information about melanoma risk than does skin complexion.
And while family history of melanoma is another important risk factor, having a parent or sibling with melanoma confers only a 2.5- to threefold increased relative risk. It's only in the much smaller subgroup of individuals with both an affected parent and sibling that the risk really soars to about ninefold.
Numerous studies have shown that dysplastic nevi are an independent risk factor for melanoma and that the relative risk climbs as the number of dysplastic nevi increases. Although risk estimates vary, two dysplastic nevi are often associated with a roughly twofold increased relative risk of melanoma, five with a five- or sixfold increased risk, and so forth.
Dysplastic nevi are present in 2%–8% of whites. They are defined clinically as nevi at least 5 mm in size with a flat component and at least two of the three following criteria: indistinct borders, variable pigmentation, and an irregular asymmetric outline. Dysplastic nevi are markers of risk, not obligate precursors. Although melanoma sometimes arises within a dysplastic nevus, the melanoma risk extends to normal-appearing skin, so there is no point in trying to prophylactically remove dysplastic nevi, he stressed.
To test the hypothesis that dermoscopic pattern might do a better job of defining patients at high risk for melanoma than might identification of clinical dysplastic nevi, Dr. Halpern and his coinvestigators assessed in unblinded fashion dermoscopic images of 187 individual nevi from the backs of 20 patients with invasive melanoma and 150 nevi from 20 age- and gender-matched controls at very high risk for melanoma. All participants had numerous moles, including multiple dysplastic nevi.
In a multivariate logistic regression analysis, the finding of what the investigators called a complex global dermoscopic pattern was associated with a highly significant 2.9-fold increase in melanoma risk. They defined a complex global pattern as one in which both a reticular pigment network and globules were seen in the lesion.
In contrast, the dermoscopic finding of dots in a nevus was associated with a 50% reduction in the likelihood of melanoma (Br. J. Dermatol. 2008 Jan. 17 [Epub doi:10.1111/j.1365-2133.2007.08404.x]).
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