Socioeconomic and Environmental Correlates of Global Lung Cancer Incidence: A Cross-Sectional Ecological Analysis of 183 Countries

Background/Objectives: Lung cancer exhibits substantial international variation in incidence that cannot be fully explained by established individual-level risk factors alone. Although tobacco smoking remains the principal cause of lung cancer, international ecological associations may also be influenced by differences in socioeconomic development, epidemiological transition, healthcare infrastructure, diagnostic capacity, and cancer registration systems. This study examined country-level associations between behavioral, environmental, occupational, dietary, metabolic, socioeconomic, and healthcare indicators and lung cancer incidence across 183 countries. Methods: An ecological cross-sectional study was conducted across 183 countries. Lung cancer incidence estimates for 2024 were obtained from the International Agency for Research on Cancer (IARC) Global Cancer Observatory, Cancer Today platform, using GLOBOCAN 2024. Exposure and contextual indicators were obtained from international databases, with reference years varying across indicators. Incidence was evaluated for the total population, males, females, and individuals aged 15–64 years. Country-level associations were assessed using exploratory Spearman correlations, exploratory receiver operating characteristic (ROC) analyses, and multivariable linear regression models. Analytical sample sizes varied according to data availability. Results: Indicators associated with socioeconomic development, including expected years of schooling (ρ = 0.664–0.728), personal health expenditure (ρ = 0.656–0.706), meat consumption (ρ = 0.640–0.732), and tobacco consumption (ρ = 0.492–0.677), showed consistent positive ecological associations with lung cancer incidence. Occupational silica exposure showed small positive ecological correlations (ρ = 0.194–0.278). Conversely, unsafe water sources (ρ = −0.729 to −0.786) and unsafe sanitation (ρ = −0.661 to −0.763) exhibited strong inverse ecological associations. Multivariable regression models explained 55.4–66.1% of the international variability in lung cancer incidence, with tobacco consumption showing positive associations across all demographic groups after adjustment for the other covariates included in the models. The inverse ecological associations observed for unsafe water and sanitation indicators may reflect differences in socioeconomic development, epidemiological transition, diagnostic capacity, and cancer registration systems; however, these explanations were not directly evaluated and should not be interpreted as evidence of biologically protective effects. Conclusions: Selected country-level indicators were associated with international variation in lung cancer incidence. Tobacco consumption showed positive associations across all demographic groups after adjustment for the covariates included in the models. The inverse ecological associations observed for unsafe water and sanitation indicators may reflect contextual differences between countries, but these explanations were not directly evaluated. The findings remain susceptible to residual confounding and do not establish individual-level causal relationships.