Chronic Obstructive Pulmonary Disease and Risk of Lung Cancer: The Importance of Smoking and Timing of Diagnosis
Authors: Laureano Molins, Àlvar Agusti
Journal: Journal of Thoracic Oncology (2013)

To the Editor: We read with interest the article by Powell et al.1Powell HA Iyen-Omofoman B Baldwin DR Hubbard RB Tata LJ Chronic obstructive pulmonary disease and risk of lung cancer: the importance of smoking and timing of diagnosis.J Thorac Oncol. 2013; 8: 6-11Crossref PubMed Scopus (59) Google Scholar on the risk of lung cancer (LC) in patients with chronic obstructive pulmonary disease (COPD). The authors literally concluded that “… a diagnosis of COPD is strongly associated with a diagnosis of LC, however, this association is largely explained by smoking habit, strongly dependent on the timing of COPD diagnosis, and not specific to COPD. It seems unlikely, therefore, that COPD is an independent risk factor for lung cancer.”1Powell HA Iyen-Omofoman B Baldwin DR Hubbard RB Tata LJ Chronic obstructive pulmonary disease and risk of lung cancer: the importance of smoking and timing of diagnosis.J Thorac Oncol. 2013; 8: 6-11Crossref PubMed Scopus (59) Google Scholar We congratulate the authors for their study but respectfully disagree regarding their interpretation of results and conclusions for the reasons explained below. Using a U.K. general practice database (Health Improvement Network), Powell et al.1Powell HA Iyen-Omofoman B Baldwin DR Hubbard RB Tata LJ Chronic obstructive pulmonary disease and risk of lung cancer: the importance of smoking and timing of diagnosis.J Thorac Oncol. 2013; 8: 6-11Crossref PubMed Scopus (59) Google Scholar identified 11,888 incident cases of LC, 23% of whom had a prior diagnosis of COPD compared with only 6% of 37,605 controls matched for age, sex, and practice. The odds ratio (OR) of LC in patients who had COPD diagnosed within 6 months of their cancer diagnosis were 11-fold those of patients without COPD (11.47, 95% confidence interval [CI]: 9.38–14.02). When, for reasons unclear to us, analysis was restricted to those cases with COPD diagnosed more than 10 years before LC diagnosis with, importantly, adjustment for smoking, the OR decreased to 2.18 (95% CI: 1.87–2.54). Given that the OR is the ratio of the odds of an event occurring in one group to the odds of it occurring in another group, we think that these remarkable results should be interpreted differently because they: (1) confirm that smoking is a major risk factor for both COPD and LC (OR: 11.47) and (2) demonstrate that, after adjusting for smoking and time since COPD diagnosis, the risk of developing LC is 2.18 times higher in smokers with COPD and that this is statistically significant (95% CI: 1.87–2.54). In other words, those smokers who are susceptible to the effects of smoking and develop COPD (not all smokers) have more than twice the risk of developing LC than smokers who manage to preserve their lung function within the normal range despite their habit. To put it simply, these results clearly show that COPD is an independent risk factor for LC. This interpretation is opposite to that offered by Powell et al.1Powell HA Iyen-Omofoman B Baldwin DR Hubbard RB Tata LJ Chronic obstructive pulmonary disease and risk of lung cancer: the importance of smoking and timing of diagnosis.J Thorac Oncol. 2013; 8: 6-11Crossref PubMed Scopus (59) Google Scholar but potentially very important in any program of LC screening2The National Lung Screening Trial Research Team Reduced lung-cancer mortality with low-dose computed tomographic screening.New Eng J Med. 2011; 365: 395-409Crossref PubMed Scopus (6876) Google Scholar in which cost–benefit ratio is proportional to the specific population screened.3Sekine Y Katsura H Koh E Hiroshima K Fujisawa T Early detection of COPD is important for lung cancer surveillance.Eur Respir J. 2012; 39: 1230-1240Crossref PubMed Scopus (99) Google Scholar