Solar ultraviolet radiation exposure, and incidence of childhood (0-19 years) malignant and non-malignant brain tumour in a US population-based dataset, 2000-2021.

Brain tumour is the second most common type of childhood cancer and the most common solid tumour in children, but its aetiology is largely unknown. Some previous studies have suggested that elevated ultraviolet radiation (UVR) exposures decrease brain tumour risk, but the evidence is inconsistent. We conducted a cross-sectional study (with census-derived population counts) to assess age < 20 malignant/non-malignant brain tumour incidence overall and for major categories in Surveillance, Epidemiology and End Results 2000-2021 data, using ground-based UVR-irradiance measures, via quasi-likelihood models accounting for over/under-dispersion, adjusted for age, sex, race/ethnicity and other socioeconomic variables. There were 29,088/18,585 cases of malignant/non-malignant brain tumour, with generally significant decreasing trends of both types of tumour with UVR irradiance [relative risk (RR) = 0.754/mW/cm2 (95% CI 0.659, 0.862, p < 0.0001) for malignant brain tumour, RR = 0.466/mW/cm2 (95% CI 0.382, 0.567, p < 0.0001] for non-malignant brain tumour), although there was significant heterogeneity by histopathologic subtype, race/ethnicity, and sex. Equally, there is a highly significant decreasing trend of both types of tumour with UVR-cumulative radiant exposure (p < 0.0001). These trends are also significant in many malignant/non-malignant brain tumour histopathological subtypes and racial/ethnic groups. However, there are certain non-malignant brain tumour subtypes, for example tumours of the pineal region and meningeal tumours, where RR significantly exceed 1 in relation to UVR irradiance (p = 0.0330, p = 0.0024 respectively). Our finding, of a generally protective effect of UVR on brain tumour risk is not clear-cut, and warrants large studies of specific histopathological pediatric/adolescent brain tumours using individual-level data on solar exposures and key effect modifiers and potential confounders.