Trends in smoking-attributable and smoking-unrelated lung cancer death rates in the United States, 1991-2018

Background In the United States, lung cancer death rates have been declining for decades, primarily as a result of pronounced decreases in cigarette smoking. It is unclear, however, whether there have been similar declines in mortality rates of lung cancer unrelated to smoking. We estimated trends in US lung cancer death rates attributable and not attributable to smoking from 1991 to 2018.Methods The study included 30- to 79-year-olds in the National Health Interview Survey who were linked to the National Death Index, 1991-2014. Adjusted hazard ratios for smoking status and lung cancer death were estimated, and age-specific population attributable fractions were calculated. Annual population attributable fractions were multiplied by annual US national lung cancer mortality, partitioning rates into smoking-attributable and smoking-unrelated lung cancer deaths. All statistical tests were 2-sided.Results During 1991-2018, the proportion of never smokers increased among both men (35.1%-54.6%) and women (54.0%-65.4%). Compared with those who had ever smoked, those who had never smoked had 86% lower risk (hazard ratio = 0.14; 95% confidence interval [CI] = 0.12 to 0.16) of lung cancer death. The fraction of lung cancer deaths attributable to smoking decreased from 81.4% (95% CI = 78.9 to 81.4) to 74.7% (95% CI = 78.1 to 71.4). Smoking-attributable lung cancer death rates declined 2.7% per year (95% CI = -2.9% to -2.5%) and smoking-unrelated lung cancer death rates declined 1.8% per year (95% CI = -2.0% to -1.5%); these declines have accelerated in recent years.Conclusions An increasing proportion of lung cancer deaths are unrelated to smoking based on declines in smoking prevalence. Smoking-unrelated lung cancer death rates have declined, however, perhaps because of decreases in secondhand smoke and air pollution exposure as well as treatment improvements.