Association of UV Radiation Exposure, Diagnostic Scrutiny, and Melanoma Incidence in US Counties

Abstract

Importance: Although UV radiation exposure is the conventionally reported risk factor for cutaneous melanoma, an alternative exposure is diagnostic scrutiny: the more physicians look for and biopsy moles, the more melanoma they find.

Objective: To assess the association of proxies for UV radiation exposure and diagnostic scrutiny with geographical patterns of melanoma incidence.

Design, setting, and participants: This was a cross-sectional ecological analysis of the 727 continental US counties reporting to the Surveillance, Epidemiology, and End Results (SEER) Program (among a total of 3108 counties). Environmental data relevant to UV radiation exposure (from a variety of sources), Health Resources and Services Administration data relevant to diagnostic scrutiny, and SEER data on melanoma incidence among the non-Hispanic White population diagnosed with melanoma from 2012 through 2016 were combined. Data analysis was performed between January 2020 and July 2022.

Exposures: Three UV radiation proxies (UV daily dose, cloud variability, and temperature variability) and 3 diagnostic scrutiny proxies (median household income, dermatologists, and primary care physician supply).

Main outcomes and measures: Melanoma incidence (in situ and invasive cancers).

Results: In total, 235 333 melanomas were diagnosed. Proxies for UV radiation exposure changed gradually across geography, while melanoma incidence and proxies for diagnostic scrutiny changed abruptly across contiguous counties. The UV daily dose, a variable the National Cancer Institute specifically developed for melanoma analyses, was uncorrelated with incidence (r = 0.03; P = .42). For context, smoking prevalence was highly correlated with lung cancer incidence in the same counties (r = 0.81; P < .001). Melanoma incidence was correlated with median household income (r = 0.43; P < .001). Counties with no dermatologists and shortages of primary care physicians had the lowest incidence, while counties amply supplied with both had the highest, despite having lower mean UV daily dose. There was little association between melanoma incidence and melanoma mortality (r = 0.09; P = .05), while the analogous association in lung cancer was strong (r = 0.96; P < .001).

Conclusions and relevance: In this cross-sectional ecological study, the current geographical pattern of melanoma incidence across US counties was less associated with proxies for UV radiation exposure and more so with proxies for diagnostic scrutiny. Incidence-the fundamental epidemiologic measure of disease frequency-now had little association with the feared outcome of melanoma: death.

Figure 1.. County-Level Data Maps

Melanoma incidence per 100 000 (2012-2016) and selected proxies for UV radiation exposure and diagnostic scrutiny in the continental US. The UV radiation exposure proxies are largely historical and thus precede cancer diagnosis. Diagnostic scrutiny proxy variables are contemporaneous with cancer diagnosis.

Figure 2.. Correlation Matrix

The matrix is ordered using hierarchal clustering with complete linkage such that similar variables are adjacent to one another—allowing readers to visualize clusters of variables with similar intragroup associations. The unit of analysis is the county (n = 727). Strength of association is indicated by circle size (larger circles represent stronger associations); association directionality is indicated by circle color (positive associations are blue, negative associations are red). Correlation coefficients (Pearson r) for melanoma incidence with other variables are shown.

Figure 3.. Scatterplots of the 727 Surveillance, Epidemiology, and End Results Counties

Incidence is age adjusted to the 2000 standard population and expressed per 100 000. Correlation coefficients (Pearson r) and simple linear regression lines are also shown.

Figure 4.. Association of Physician Supply and Melanoma Incidence in 727 US Counties

A, Dermatologists. Most US counties do not have a dermatologist, a pattern that is replicated in the counties reporting to the Surveillance, Epidemiology, and End Results Program. Individuals who travel to a different county to see a dermatologist and who then receive a diagnosis of melanoma will nonetheless have their melanoma diagnosis attributed to their county of residence. B, Primary care physicians. The US Bureau of Health Workforce defines primary care shortage areas as geographic areas with more than 3000 to 3500 individuals per primary care physician. We distinguish counties using a threshold within this range, a threshold that translates to 30 primary care physicians per 100 000. C, Three levels of diagnostic scrutiny resulting from variable physician supply. Low refers to counties with primary care shortages and without dermatologists (12 of the 163 counties that met the shortage definition had an active dermatologist, and thus there were 151 counties in this group); medium refers to counties well supplied with primary care, but without dermatologists; and high refers to counties with dermatologists.

Figure 5.. Association Between Melanoma Incidence and Mortality in 469 US Counties

Melanoma incidence and mortality are restricted to White individuals; lung cancer incidence and mortality are restricted to men. Both plots use the same 16-year time frame and the same 469 US counties with 10 or more deaths for each cancer. Incidence (2001-2016) and mortality (2002-2017) are both age adjusted to the 2000 standard population and expressed in terms of diagnoses/deaths per 100 000. Correlation coefficients (Pearson r) and simple linear regression lines are also shown. Two extremes of melanoma incidence—Lea County, New Mexico, and Summit County, Utah—appear as orange dots.