Malignant melanoma in childhood has been gradually rising, though it’s still rare, a population-based study affirmed.

Incidence among white children in the U.S. rose by an average 2% per year since 1973 to reach 6.0 per million in 2009, Kimberly Johnson, MPH, PhD, of Washington University in St. Louis, and colleagues found.

Their analysis of the Surveillance, Epidemiology, and End Results (SEER) database didn’t point to too much sun as a driver, the group reported in the May issue of Pediatrics.

Instead, the increase appeared to be greatest among those expected to have low exposure to sunburn-inducing UV-B rays due to living in northern latitudes, as well as among girls and 15- to 19-year-olds.

One factor that could explain why those three groups were at particular risk is UV-A exposure from tanning beds, Johnson’s group suggested.

Not only did the indoor tanning industry spring up in the 1970s, but teens have the highest prevalence of use, they pointed out.

“In addition to girls being more likely to tan indoors than boys, cities with higher percentages of whites and lower UV index scores have significantly higher densities of indoor tanning facilit[ies],” the authors wrote.

Other possible explanations might be changes in how melanoma cases are ascertained, and even overdiagnosis.

Similar upward trends in malignant melanoma have been shown in adults, young women, and in two pediatric studies through the early 2000s.

“Despite increasing rates, we note that malignant melanoma survival rates have increased since the 1970s,” Johnson’s group pointed out. “Five-year survival is currently nearly 100% for cases diagnosed in localized stages versus 82% for cases diagnosed in regional or distant stages. These data emphasize the importance of early detection.”

The SEER database included 1,230 white young people, ages 20 and under, with primary malignant melanoma in nine cancer registries from 1973 through 2009.

So few cases occurred among other ethnic or racial groups that they were excluded.

Age-adjusted melanoma incidence rose over the study period by an average 2% per year among boys and 2.2% per year among girls without any significant turning points.

Unlike in adults, the incidence ratio was 1.6 times higher in girls than in boys (7.4 versus 4.6 per million).

That gender difference was consistent across age groups, although the melanoma incidence rose with age overall:

  1.1 per million before age 10
  3.6 per million in 10- to 14-year-olds
  18.0 per million in 15- to 19-year olds

The year-over-year increase was only significant in the two older age groups at 2.9% and 1.9%, respectively.

While the incidence of childhood melanoma was higher in the registries covering high UV-B areas further south compared with those in low exposure areas further north (6.7 versus 5.4 per million), the trend for change followed the opposite pattern.

Low UV-B areas had fairly stable rates over time, whereas the low UV-B areas saw an annual percent change of 3.7% from 1973 through 2009.

But the significant upswing occurred in tumor sites where sun exposure would occur:

  4.5% per year for the skin on unspecified parts of the face
  2.8% for the trunk
  2.6% for the lower limbs and hip

The only downward trend among all the analyses was among 15- to 19-year-olds in high UV-B exposure areas starting in 1985 (–1.5% per year).

The shift toward sentinel lymph node biopsies during the study period would have contributed to regional upstaging, but wouldn’t have accounted for the overall increase in incidence, the researchers noted.

Study limitations included lack of data on individual outdoor UV exposure, indoor tanning, familial factors, or thickness of lesions to draw inferences about causes of the trends, and inability to rule out an influence of changes in diagnosis patterns over time.

Primary source: Pediatrics
Source reference: Wong JR, et al. “Incidence of Childhood and Adolescent Melanoma in the United States: 1973–2009” Pediatrics 2013;131.