Features of COPD as Predictors of Lung Cancer

To the Editor:

With great interest, we read the article by Carr and colleagues¹ in CHEST (June 2018) on features of COPD as predictors of lung cancer, as we have also been interested in the coexistence of these two diseases.^{2, 3} We would like to hear the authors’ comments regarding the following three points. First, the authors described the severity of airflow obstruction as an independent risk factor for lung cancer.¹ We would like to hear from the authors whether we should consider the susceptibility to lung cancer had close relationship with that to COPD, or whether airflow limitation was related to susceptibility to lung cancer. Second, the authors also concluded that a history of acute respiratory exacerbations increased the risk of small-cell lung cancer (SCLC) history. It is a well-known fact that SCLC and squamous cell carcinoma have a relationship with the smoking habit. Please explain why a history of acute respiratory exacerbations increased only the risk of SCLC history. Finally, in connection with the first question, if airflow limitation is associated with the onset of lung cancer, we would like to know whether airflow limitation is related to the peripheral development of lung cancer rather than central development.