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Etiologic and Other Factors Predicting Nevus-Associated Cutaneous Malignant Melanoma

¹ Division of Preventive Oncology, Cancer Care Ontario; ² RK Schachter Dermatology Centre, Sunnybrook and Women's College Health Sciences Centre, Toronto, Ontario, Canada; ³ School of Public Health, The University of Sydney, Sydney, New South Wales, Australia; ⁴ Cancer Control Research Program, British Columbia Cancer Agency, Vancouver, British Columbia, Canada; and ⁵ Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada

Requests for reprints: Mark P. Purdue, Division of Cancer Epidemiology and Genetics, Occupational and Environmental Epidemiology Branch, National Cancer Institute, 6120 Executive Boulevard, EPS 8111, Rockville, MD 20852. Phone: 301-451-5036; Fax: 301-402-1819. E-mail: purduem{at}mail.nih.gov

Cutaneous malignant melanomas with histologic evidence of an associated nevus (N+) may have a different risk factor profile from that of melanomas without it (N–). To address this question, a case-only analysis of 932 people with cutaneous malignant melanoma was done to identify etiologic and other factors associated with N+ melanoma. Evidence of an associated nevus was found in 36% of melanomas. N+ melanomas were thinner (P_trend = 0.0009) and more likely to be of the superficial spreading type than other types of melanoma. Subjects with N+ melanomas were younger (P_trend < 0.0001) and reported a higher nevus density on their skin than subjects with N– melanomas [odds ratio (OR), 3.1; 95% confidence interval (CI), 1.6-6.0, for high nevus density versus no nevi]. Indicators of high accumulated sun exposure were less prevalent among subjects with N+ melanomas (OR, 0.3; 95% CI, 0.2-0.4, for melanoma location on the head and neck versus location on trunk; OR, 0.2; 95% CI, 0.1-0.4, for severe solar elastosis adjacent to the melanoma versus no elastosis; OR, 0.2; 95% CI, 0.1-0.4, for lentigo maligna melanoma subtype versus superficial spreading subtype). With the exception of solar elastosis and age, all of the aforementioned variables remained significantly associated with N+ melanomas in multivariate analyses. No associations with self-reported measures of sun exposure, sunburn, or pigmentation phenotype were apparent. Our findings provide some support for the hypothesis of etiologically separate pathways for melanoma, with N+ melanomas appearing less likely to develop in the presence of characteristics suggesting high accumulated sun exposure than N– melanomas. However, it is possible that high UV exposure causes involution of nevi, thus reducing the density of nevi in exposed skin and thereby the probability of N+ melanoma.