While the overall incidence of invasive melanoma among Americans has risen between 2006 and 2015, incidence has decreased in adolescents and young adults (individuals aged 10 to 29 years at diagnosis), a recent study in JAMA Dermatology showed.1 Although experts disagree about the cause for the decline among younger cohorts, the findings are, on the whole, welcome news.

“We were both very excited and really surprised to see that in the younger groups, the adolescents and young adults, both for men and women, we’re seeing a more sustained trend and a decreasing in the incidence of melanoma,” said Jennifer M. Gardner, MD, a coauthor of the study and assistant professor in the division of dermatology at the University of Washington, Seattle.

The study was based on an analysis of 382,533 histologically confirmed cases of invasive melanoma reported through the US National Program of Cancer Registries-Surveillance Epidemiology and End Results (SEER) combined database between 2006 and 2015.

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The researchers then determined annual incidence rates of invasive melanoma in different age cohorts. Over the study period, the overall incidence rate of melanoma rose from 200 cases per million person-years to nearly 230 cases per million person-years. In adults 40 years or older, the annual percentage change was 1.8 over the study period. In contrast, rates for children younger than 9 years remained low and relatively stable over the study period.

The researchers found statistically significant declines in melanoma incidence for adolescents and young adults. For individuals aged between 10 and 19 years, incidence rates fell by an annual percentage change of -4.4% for adolescent boys, and -5.4% for adolescent girls. For adults aged between 20 and 29 years, that figure was -3.7% for men, and -3.6% for women.

In an analysis of cases documented since 2000, the team observed that incidence rates for adolescents and young adults had peaked around 2004 to 2005, and have been decreasing since.

At first glance, these results appear to conflict with the findings of another recent study that describes an increasing rate of head and neck melanoma between 1995 and 2014 among pediatric, adolescent, and young adult populations in the US and Canada, particularly as they relate to male individuals.2

To Dr Gardner, however, the 2 studies are compatible. Based on an unpublished analysis by her research group that focused on head and neck melanomas specifically, they also found there was an increased risk for disease in adolescent boys and young men compared with their female counterparts, a contrast to the overall melanoma pattern in that age cohort, where younger women are more at risk than boys or young adult men. However, examining trends over the whole study period, “we do still see that there was a peak in incidence and [then] a downtrend even in those groups for head and neck melanoma, specifically,” she said. Dr Gardner also pointed out that the 2 studies differ in the number of cases, study period, and the age range specifications of the cohorts that were examined.

The main limitations of the new research is the lack of available data on the study patients’ characteristics, such as skin pigmentation and sun protection history, making it impossible to determine whether any incidence decreases across cohorts could be explained by sun-protective behavior or possible demographic changes among younger populations.

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Nevertheless, in an effort to account for demographic change, the researchers examined melanoma trends among non-Hispanic white individuals — which to Dr Gardner, represented the “best available surrogate” for skin pigmentation — and compared those findings with those of the general population. If rates among non-Hispanic white individuals were stable or increasing, that could suggest that the decline in incidence seen may be partially driven by demographic changes. However, they found that melanoma incidence rates for non-Hispanic white individuals broadly reflected those of the general population.

Based on this, Dr Gardner and her colleagues posited that the most likely explanation for the decrease in melanoma incidence in younger cohorts was the result of the public health campaigns that started in the late 1990s and early 2000s encouraging the adoption of sun-protective behaviors, such as the use of sunscreen and protective clothing.

Sun protection over the course of a person’s lifetime is likely a key risk factor for developing melanoma later in life, she explained. “Older populations may not have gotten into sun-protecting or ultraviolet (UV)-protecting habits until later in life,” which would explain why recent health interventions may have had little impact on melanoma incidence for older cohorts, she said.