Melanoma threats from ultraviolet exposure vary by state
Authors: Mike Fillon
Journal: CA A Cancer Journal for Clinicians (2020)

Cutaneous melanoma has one of the fastest growing incidence rates of any cancer in the United States, having increased by 2% per year among both sexes between 2011 and 2015. However, a new study in the International Journal of Cancer (published online February 17, 2020. doi:10.1002/ijc.32921) may better equip state officials to create strategies that help slow and reverse this trend. Researchers from the American Cancer Society (ACS) investigated the proportion of incidence and the incidence rates of malignant melanomas caused by ultraviolet (UV) radiation in each state. For the study, they calculated the difference between the states' melanoma incidence rates from 2011 to 2015 among non-Hispanic whites versus, as a baseline, white individuals living in Connecticut from 1942 to 1954. “Although the burden of UV-attributable melanoma varied across states, it's important to note that the burden was considerably high in all states,” says lead author, Farhad Islami, MD, PhD, a cancer epidemiologist and scientific director of surveillance research at the ACS. According to Dr. Islami, in general, cancer cases attributable to a risk factor are calculated as the difference between the observed cases in an exposed cohort and the cases expected in the cohort based on an unexposed population. However, that was not possible in this study “because there is no population completely unexposed to UV radiation,” he says. For that reason, previous studies used melanoma incidence rates in certain populations as reference rates associated with theoretically minimum UV exposure. One commonly used reference rate is the rate among US blacks or rates in some African countries because black individuals are much less susceptible to UV-related melanomas because increased melanin in their epidermis reduces the deleterious effects of UV radiation. Another common approach incorporates rates estimated by modeling using observed incidence rates between 1960 and 1997 from the South Thames region of England for the cohort born in 1903. “However, there were some concerns about the appropriateness of using these reference rates to estimate the burden of melanoma attributable to UV radiation in the US,” Dr. Islami says. “For example, there could be some other important biological (eg, genetic) differences between blacks and other racial groups in terms of melanoma occurrence, so that melanoma rates in blacks may not be representative rates for those with minimal UV exposure in other groups.” To overcome these concerns, ACS researchers applied a new method. They identified and used observed, and not modeled, historical melanoma incidence rates from Connecticut as their reference. Connecticut had the first statewide population-based cancer registry in the United States, which was established in 1935, and has a high-latitude environment with a lower rate of UV exposure and a very low incidence rate of melanoma. Moreover, the investigators used Connecticut's melanoma incidence rates from 1942 to 1954, which were approximately 10 times lower than current rates. The rate was less than 2.3 per 100,000 population before 1955, whereas it was 20.5 per 100,000 population in 2012 through 2016. “Indeed, for most adults, melanomas diagnosed during 1942-1954 likely reflected UV exposure accumulated in the 1930s or earlier, when exposure was likely minimized by clothing style with more complete skin coverage and limited recreational exposure,” says Dr. Islami. According to Dr. Islami, the variations across states likely reflect a combination of differences in the strength of solar UV radiation (commonly measured as the UV index), participation in outdoor activities, sun protection, indoor tanning, and early detection activities. “However, it is difficult to measure the contribution of each factor to variations in UV-attributable melanoma by state because representative statewide data for most of these factors are lacking,” he says. Nationally, previous studies have shown that engagement in outdoor recreational activities has increased substantially during recent decades, and that sun protection use is suboptimal. “Differences in participation in indoor tanning may also have contributed to variations in the burden, notably among younger women,” Dr. Islami says. The UV index varies across states. It generally is higher in areas closer to the equator, although other factors such as altitude also can influence it. UV exposure in areas with a higher UV index is likely to cause sunburns more quickly. And, with the same duration of sun exposure and the same extent of sun-protective behaviors, individuals in higher UV index areas may be at a higher risk of melanoma compared with those in other areas. However, the researchers note that even in states with a very high UV index, the risk of melanoma can be minimized by avoiding excessive sun exposure, whereas individuals in areas with a relatively low UV index could be at high risk if they are frequently engaged in outdoor activities with insufficient sun protection. Because the study found that greater than 90% of melanoma cases in the United States are attributable to UV radiation, the researchers believe that many melanoma cases are preventable by avoiding excessive UV exposure. “While we may have little control over the UV index, other major contributing factors to melanoma risk, including UV exposure behaviors such as outdoor activities and indoor tanning and sun protection use, are modifiable,” Dr. Islami says. Other recommendations endorsed by the ACS to protect the skin include seeking shade when possible; avoiding sunbathing; limiting outdoor activities during times of peak sunlight and wearing protective clothing, hats, and sunglasses; using appropriate sunscreens; and avoiding indoor tanning. “People should also talk to their doctors if they notice any of the warning signs, also known as the A-B-C-D-Es of melanoma,” Dr. Islami says. That includes skin moles or spots that are asymmetrical, have a border that is irregular or jagged, are uneven in color, have a diameter larger than the size of a pea, or appear to be evolving, with changes to shape, size, or other symptoms. Beyond that, Dr. Islami says representative statewide data are needed regarding determinants of variations in melanoma incidence rates, such as sun protection use and melanoma screening. “More research is also needed on interventions to increase sun safety behaviors, because current interventions have shown relatively modest effects in the US, and on the effects of interventions on clinical targets, such as sunburns and melanoma incidence,” he says. He notes that previous studies mainly have examined the effects of interventions on sun protection behaviors rather than clinical outcomes. In addition to results for non-Hispanic white individuals, the study provided information for all races/ethnicities combined, but “other racial/ethnic groups were not considered separately due to sparse data in many states,” Dr. Islami says. “However, about 13% of non-Hispanic blacks and 30% of Hispanics in the United States experience sunburn each year, with higher proportions among youth in some high exposure areas, underscoring that excessive UV exposure prevention should not be limited to whites only.” Dr. Islami adds that more research also is needed concerning the mechanisms of development and progression of melanoma, which could result in the identification of molecular targets for treatment. He also points out that the US Surgeon General and the Centers for Disease Control and Prevention have recommended multiple interventions to reduce excessive sun exposure in different settings, including schools, workplaces, and communities (eg, including sun protection in student athletic activities or providing structures or shade trees in high-use outdoor areas). “Unfortunately, these interventions have not been systematically implemented in many places,” he says. What is more, although many states have banned indoor tanning for minors aged younger than 18 years, many other states have not. ”Our results provide further evidence underscoring the importance of broad implementation and enforcement of preventive measures across all states—once again, the burden is considerably high in all states—with priority for states with higher burden,” Dr. Islami says. Photo Credit: Nataly Moskovka/Shutterstock