BACKGROUND: Patients with primary cutaneous melanoma are at increased risk for subsequent new primary melanomas. Indoor tanning is a recognized risk factor for melanoma. This study was aimed at determining the association between indoor tanning and the occurrence of multiple primary melanoma. METHODS: This was a retrospective case-control study of cases with multiple primary melanoma and sex-matched controls with single primary melanoma retrieved at a 1:2 ratio from the Biological Sample and Nevus Bank of the Melanoma Center of the University of Pittsburgh Cancer Institute. Logistic regression models were used to examine the association between multiple primary melanoma and risk factors. RESULTS: In total, 330 patients (39.1% men) with a median age of 51 years were enrolled. Compared with patients who had a single primary melanoma, patients with multiple melanomas were younger at the diagnosis of their first primary melanoma and were more likely to be discovered at stage 0 or I and to have had indoor tanning exposure, a family history of melanoma, atypical moles, dysplastic nevi, and a Breslow thickness less than 1 mm. Compared with patients' first melanomas, subsequent melanomas were more likely to be thinner or in situ. The estimated probability of the locus for the second primary being the same as that for the first primary melanoma was 34%. In a multivariate analysis after adjustments for age, a family history of melanoma, the presence of atypical and dysplastic nevi, and recreational sun exposure, indoor tanning remained significantly associated with the occurrence of multiple primary melanoma (odds ratio, 2.75; 95% confidence interval, 1.07-7.08; P = .0356). CONCLUSIONS: Indoor tanning is associated with an increased risk of second primary melanoma. Subsequent melanomas are more likely to be thin or in situ and to occur in different anatomic locations.
