Cigarette smoke is the major cause of lung cancer, the leading cause of cancer death, and of chronic obstructive pulmonary disease, the fourth leading cause of death in the United States. Using high-density gene expression arrays, we describe genes that are normally expressed in a subset of human airway epithelial cells obtained at bronchoscopy (the airway transcriptome), define how cigarette smoking alters the transcriptome, and detail the effects of variables, such as cumulative exposure, age, sex, and race, on cigarette smoke-induced changes in gene expression. We also determine which changes in gene expression are and are not reversible when smoking is discontinued. The persistent altered expression of a subset of genes in former smokers may explain the risk these individuals have for developing lung cancer long after they have discontinued smoking. The use of gene expression profiling to explore the normal biology of a specific subset of cells within a complex organ across a broad spectrum of healthy individuals and to define the reversible and irreversible genetic effects of cigarette smoke on human airway epithelial cells has not been previously reported.A pproximately 1.25 billion people smoke cigarettes daily worldwide (1). Cigarette smoking is responsible for 90% of all lung cancers, the leading cause of cancer deaths in the United States and the world (2, 3). Smoking is also the major cause of chronic obstructive pulmonary disease (COPD), the fourth leading cause of death in the United States (4). Despite the well established causal role of cigarette smoking in lung cancer and COPD, only 10-20% of smokers actually develop these diseases (5). Few indicators of which smokers are at highest risk for developing either lung cancer or COPD exist, and it is unclear why individuals remain at high risk decades after they have stopped smoking (6).Given the burden of lung disease created by cigarette smoking, surprisingly few studies (7, 8) have been done in humans to determine how smoking affects the epithelial cells of the pulmonary airways that are exposed to the highest concentrations of cigarette smoke or what smoking-induced changes in these cells are reversible when subjects stop smoking. With the two exceptions noted above, which examine a specific subset of genes in humans, studies investigating the effects of tobacco on airway epithelial cells have been in cultured cells, in human alveolar lavage samples in which alveolar macrophages predominate, or in rodent smoking models [summarized by Gebel et al. (9)]. Several recent studies have used DNA microarray technology to study normal and cancerous whole lung tissue and have identified molecular profiles that distinguish the various subtypes of lung cancer and predict clinical outcome in a subset of these patients (10-13).Based on the concept that genetic alterations in airway epithelial cells of smokers represent a ''field defect'' (14, 15), we obtained human epithelial cells at bronchoscopy from brushings of the right main bronchus proximal to the right ...

Lung cancer is the leading cause of death from cancer in the US and the world. The high mortality rate (80-85% within 5 years) results, in part, from a lack of effective tools to diagnose the disease at an early stage. Given that cigarette smoke creates a field of injury throughout the airway, we sought to determine if gene expression in histologically normal large-airway epithelial cells obtained at bronchoscopy from smokers with suspicion of lung cancer could be used as a lung cancer biomarker. Using a training set (n = 77) and gene-expression profiles from Affymetrix HG-U133A microarrays, we identified an 80-gene biomarker that distinguishes smokers with and without lung cancer. We tested the biomarker on an independent test set (n = 52), with an accuracy of 83% (80% sensitive, 84% specific), and on an additional validation set independently obtained from five medical centers (n = 35). Our biomarker had approximately 90% sensitivity for stage 1 cancer across all subjects. Combining cytopathology of lower airway cells obtained at bronchoscopy with the biomarker yielded 95% sensitivity and a 95% negative predictive value. These findings indicate that gene expression in cytologically normal large-airway epithelial cells can serve as a lung cancer biomarker, potentially owing to a cancer-specific airway-wide response to cigarette smoke.