It’s winter in North America, so few people will be sunbathing at the moment. Warm weather is coming, however, and Americans will once head to beaches and backyards, get their shirts off, and, regrettably, increase their lifetime chances of melanoma.
Interestingly, this increase won’t be uniform across the country. Some states have high overall rates of melanoma, and some don’t, at least by comparison.
This should be reasonable to anyone who reflects for a moment on geographic and lifestyle differences between, say, Florida and Alaska. But it’s not straightforward. There are population differences to consider, and other things, that make the question of what areas are worst and best very complicated, and the final answers surprising.
That’s the substance of a paper published just this week in the International Journal of Cancer.1
Farhad Islami, and a team from the American Cancer Society and Harvard University, set out to explore this, noting that there was oddly little information about the distribution of melanoma across the country yet, at least the melanomas attributable to ultraviolet radiation (which is most of them).
They gathered and analyzed health records from every state, and the District of Columbia, between 2011 and 2015, and sorted by 5-year age groups, and sex, and region, with sub-analyses for non-Hispanic white people, the part of the population most at risk of sun-induced skin cancer. The fact that melanoma rates are significantly lower in minority populations made the statistical mathematics difficult. But the team developed a normalized national reference rate that satisfied them, and they counted away.
They found that 91% of all new melanoma diagnoses during the period were attributable to sun exposure. They found that young men develop melanoma more often than young women do, but that this reverses after age 45. The people most likely to have a melanoma were the older ones, presumably having accumulated more years of exposure, with many of those years in the time before we knew about the sun-and-cancer connection.
And where were these people? Coastal areas, for the most part, but with some startling exceptions.
Hawaii was far and away the state with the most melanomas per person, and Alaska was the state with fewest, also by far. The coastal states of New Hampshire, New Jersey, Delaware, Maryland, the Carolinas, Georgia, and Florida, and California, Oregon, and Washington, tended toward the high end of the scale. Surprisingly, so did the Rocky Mountain states of Utah (almost the highest of the group), Idaho, and Colorado, and the inland states of Vermont, Kentucky, Alabama, and even snowy Minnesota.
Why the variation, is the basic question. Islami and his team suggest that it’s a function of different sunlight strength and different habits in outdoor exposure. Data is lacking for much of this, so it’s hard to know. It might also be that some states overscreen for melanoma, and report higher numbers than other states do. Genetics play a big role as well. People with different skin types develop melanoma at different rates. But just how this works, and how to adjust for it statistically, has not yet been worked out. Migration among states might be another mathematical complicator, too, particularly when it involves states with sparse populations. Data for this barely exists.
It’s a very interesting study. Overall prevalence rates show that no matter what the state, melanoma is among us in a big way. But it also shows that where (and how) people live plays quite a part in how big that presence is.
1 Islami F, et al., Cutaneous melanomas attributable to ultraviolet radiation exposure by state. Int J Cancer. 2020 Feb 17. doi:10.1002/ijc.32921. [Epub ahead of print]
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