A high number of moles and a high genetic predisposition are more strongly associated with second than first primary melanomas, according to a study published online Nov. 23 in JAMA Dermatology .

Catherine M. Olsen, Ph.D., from the QIMR Berghofer Medical Research Institute in Herston, Australia, and colleagues compared the clinical characteristics of first and second melanomas in a prospective cohort study involving men and women aged 40 to 69 years recruited in 2011 and followed until December 2018. Data were included for 38,845 patients.

The researchers found that 3.1 and 0.6 percent of participants had a single primary melanoma diagnosis and a second primary melanoma diagnosis, respectively, during a median follow-up of 7.4 years. Compared with first melanomas, second melanomas were more likely to be in situ; for invasive tumors, second versus first melanomas were more likely to be thin (≤1 mm). Having many moles at age 21 years was more strongly associated with second than first primary melanomas (hazard ratio, 6.36 versus 3.46). Furthermore, a high genetic predisposition was more strongly associated with second versus first melanoma (hazard ratio, 3.28 versus 2.06). A history of multiple skin cancer excisions was also more strongly associated with second versus first melanomas (hazard ratio, 2.63 versus 1.86). Similarly elevated associations with first and second melanomas were seen for all other phenotypic characteristics and sun exposure measures.

"Findings suggest that people who develop second primary melanomas have more nevi and greater genetic risk than people who develop only one melanoma," the authors write.

Two authors disclosed financial ties to pharmaceutical companies.

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