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BACKGROUND: Paradoxically, some studies have found that high sun exposure, a well-known cause of melanoma, is associated with lower mortality among melanoma patients. In the Norwegian Women and Health cohort, we aimed to investigate associations between pre-diagnosis sun exposure and melanoma-specific and overall death, and the potential impact of unmeasured confounding and selection bias (conditioning on melanoma diagnosis) on any observed association between markers of high sun exposure and death. METHODS: We estimated hazard ratios (HRs) by Cox regression, observed covariate E-values, bias-adjusted HRs, and performed frailty analysis. RESULTS: ≤0.001), but not for sunbathing vacations (HR=0.69, 95%CI=0.37-1.27, melanoma-specific death). Neither the E-value approach nor bias-adjusted HRs suggested a large degree of unmeasured confounding for the sunburn-death association. However, frailty analysis suggested that selection may partly explain the association. CONCLUSION: While sunburns appear protective, this association might reflect unobserved heterogeneity in melanoma risk and selection bias, and the associations may not represent a true causal effect.
Perrier et al. (Tue,) studied this question.