Trends in smoking-attributable and smoking-unrelated lung cancer death rates in the U.S., 1991-2018

Background In the U.S., lung cancer death rates have declined for decades, primarily due to pronounced decreases in cigarette smoking. However, it is unclear whether there have been similar declines in mortality rates of lung cancer unrelated to smoking. We estimated trends in U.S. lung cancer death rates attributable and not attributable to smoking from 1991-2018. Methods The study included 30-79-year-olds in the National Health Interview Survey who were linked to the National Death Index, 1991-2014. Adjusted hazard ratios (HRs) for smoking status and lung cancer death were estimated, and age-specific population attributable fractions (PAFs) were calculated. Annual PAFs were multiplied by annual U.S. national lung cancer mortality, partitioning rates into smoking-attributable and smoking-unrelated lung cancer deaths. All statistical tests were two-sided. Results During 1991-2018, the proportion of never smokers increased among both men (35.1% to 54.6%) and women (54.0% to 65.4%). Compared to ever smokers, never smokers had 86% lower risk (HR = 0.14; 95%CI 0.12, 0.16) of lung cancer death. The fraction of lung cancer deaths attributable to smoking decreased from 81.4% (95%CI 78.9, 81.4) to 74.7% (95%CI 78.1, 71.4). Smoking-attributable lung cancer death rates declined 2.7%/year (95%CI -2.9, -2.5) and smoking-unrelated lung cancer death rates declined 1.8%/year (95%CI -2.0, -1.5); these declines accelerated in recent years. Conclusions An increasing proportion of lung cancer deaths are unrelated to smoking, due to declines in smoking prevalence. However, smoking-unrelated lung cancer death rates have declined, perhaps due to decreases in secondhand smoke and air pollution exposure and treatment improvements.