Background <p>Lung adenocarcinoma diagnoses have increased globally despite declining tobacco exposure, raising questions about non–tobacco-related contributors. The role of fine particulate matter (PM2.5) peaks related to biomass burning in shaping population-level lung cancer patterns remains unexplored.</p> Methods <p>An ecological analysis was conducted across the Regional Health Departments of São Paulo State, Brazil, from 2000 to 2023. Histologically confirmed lung cancer cases were obtained from the state cancer registry. Temporal trends in the adenocarcinoma-to-total lung cancer ratio (ATR) were evaluated alongside annual mean and maximum PM2.5 concentrations and wildfire counts derived from satellite data.</p> Results <p>Among 51,580 lung cancer cases, adenocarcinoma accounted for 36%. Regions with a significant increase in ATR demonstrated annual increases ranging from 0.39 to 0.72%. With the exception of the São Paulo metropolitan area, which showed high mean PM2.5 levels despite low wildfire activity, all other regions with increasing ATR exhibited substantially higher wildfire occurrence (311 vs. 207 annual hotspots; <i>p</i> = 0.049), which strongly correlated with PM2.5 peaks (<i>ρ</i> = 0.928, <i>p</i> = 0.007). Periods of elevated PM2.5 peaks consistently coincided with increased wildfire activity.</p> Conclusions <p>These findings suggest that biomass-burning–related PM2.5 peaks may be relevant to population-level patterns of lung cancer epidemiology.</p>