By Linda Carroll

(Reuters Health) – Rates of melanoma caused by exposure to the sun’s ultraviolet (UV) rays vary widely from state to state, a new U.S. study suggests.

Researchers found the highest rates in Hawaii and on the East and West coasts, but also in a few landlocked states, such as Vermont and Minnesota, according to the results published in the International Journal of Cancer.

“Overall, even in states with a lower burden of cancer, the numbers are still high,” said the study’s lead author, Dr. Farhad Islami, director of surveillance research at the American Cancer Society. “As previous research has shown, over 90% of those cancers are from UV and the main source of that is exposure to the sun and indoor tanning. So essentially, most of them are preventable.”

Islami and his colleagues found melanoma rates ranged from 15 cases per year in Alaska to 65 per year in Hawaii and attributed the differences to a combination of factors, including the strength of the sun’s rays, variations in the amount of time people spent in outdoor activities and the use of indoor tanning salons.

To get a sense of how melanoma rates might have changed over time and how they might vary from place to place, the researchers first sought to establish a baseline by looking at the number of melanomas recorded between 1942 and 1954 by the state of Connecticut, which established the first statewide population-based cancer registry in the U.S.

Islami and his colleagues assumed that most of the melanomas recorded in Connecticut in the early 40s and 50s would not be related to sun exposure because of the state’s more northern latitude and because melanomas diagnosed in that time period would reflect sun exposure accumulated in the 1930s or earlier, when clothing styles offered more complete skin coverage. That meant that the Connecticut numbers could work as a stand-in for minimal UV exposure, Islami said.

For more recent melanoma statistics, the researchers turned to a U.S. database of newly-diagnosed cancer cases, focusing on melanomas reported between 2011 and 2015.

After comparing recent melanoma rates to those from the Connecticut baseline, and accounting for patient age, the researchers found that 94.3% of cases were among non-Hispanic white people, and that UV exposure could explain 91% of the total between 2011 and 2015, or 338,701 of 372,335 cases nationwide.

Overall, melanoma rates are lowest among people with darker skin, and among black people in the U.S. the incidence is 1 case per 100,000 population, while among Hispanic people the rate is 4.5 per 100,000 and among non-Hispanic whites it’s 27 per 100,000, the study team notes.

To avoid capturing variations in the incidence of melanomas that were due to differences in state racial makeup, the researchers focused on rates among non-Hispanic whites and found that multiple states along the East and West coasts had UV-attributable incidence rates exceeding 25 per 100,000. Delaware came in at 37.1 per 100,000; Georgia, at 36.5; California at 33.8; Maryland at 32.6; North Carolina at 29.5; Florida at 29.2; Oregon at 28.5; South Carolina at 28.1; Washington at 27.8; New Jersey at 27.7 and New Hampshire at 26.5.

Rates were also above 25 per 100,000 in several inland states: Utah came in at 40.4 per 100,000; Vermont at 31.4; Minnesota at 27.9; Idaho at 27.6 and Kentucky at 25.7.

“People in many states located on the East and West coasts tend to go to the beaches,” Islami said. “In states like Utah, people spend a lot of time skiing or engaged in other outdoor activities.”

While the new study is interesting and underscores the importance of minimizing UV exposure, it does make a number of assumptions, said Dr. Laura Ferris, an associate professor of dermatology at the University of Pittsburgh School of Medicine and director of clinical trials for UPMC dermatology.

First, the authors are assuming that only sun exposure has changed over the years and that residents of Connecticut in the 30s weren’t getting much sun – that probably doesn’t apply to farmers and other people working outside, Ferris said. Second, the authors are assuming that people spent their entire lives in the state in which they were diagnosed, she added.

Third, although the authors acknowledge the possibility that doctors are more tuned in to the possibility of melanoma now and are thus diagnosing more, it’s not clear what impact melanoma screening has had on diagnosis rates, Ferris said. “If you look at other cancers, the rates are always higher in groups that get screened.”

SOURCE: International Journal of Cancer, online February 17, 2020.