Multiple moles, genetic predisposition up risk of second primary melanomas

Individuals with multiple nevi and high genetic predisposition to melanoma appear to have the highest risks of developing second primary melanomas, according to a study.

In this population-based prospective cohort study, researchers recruited 38,845 adults (mean age at baseline 56.1 years; 54.2 percent women) in Queensland, Australia. Demographic, phenotypic, sun exposure, and genetic factors were examined in relation to the risks of developing one or multiple melanomas.

Over a median follow-up period of 7.4 years, 1,212 (3.1 percent) participants had a single primary melanoma diagnosis and 245 (0.6 percent) had a second primary melanoma diagnosis. Compared with first melanomas, second melanomas tended to be in situ as well as thinner (ie, ≤1 mm) as invasive tumours.

The presence of many moles at age 21 years (self-reported using visual scoring tool) had a stronger association with second (hazard ratio [HR], 6.36, 95 percent confidence interval [CI], 3.77–10.75) than first primary melanoma (HR, 3.46, 95 percent CI, 2.72–4.40; p=0.01 for the difference between HRs).

Likewise, a high genetic predisposition (ie, polygenic risk score in tertile 3) showed a stronger association with second (HR, 3.28, 95 percent CI, 2.06–5.23) than first melanoma (HR, 2.06, 95 percent CI, 1.71–2.49; p=0.03).

A history of multiple skin cancer excisions was also associated with a higher risk of second (HR, 2.63, 95 percent CI, 1.80–3.83) than first melanomas (HR, 1.86, 95 percent CI, 1.61–2.16; p=0.05).

Other phenotypic characteristics and sun exposure measures were positively correlated with both second and first melanomas, with no significant difference.