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

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.