Smoking is the major cause of lung cancer and is also known to cause various other diseases, including diabetes and cerebral cardiovascular diseases. In particular, smoking is closely related to COPD. This study investigated quality of life and symptoms of COPD and analyzed how COPD affected prognosis in patients with advanced NSCLC. The results confirmed that patients with advanced NSCLC and COPD had more symptoms and reduced quality of life in several aspects, but these did not affect the survival rate in the patients. In this study, the prevalence of COPD was 50.5% among all patients with advanced NSCLC. Several studies have focused on the frequency of COPD in lung cancer: Ytterstad et al. reported that 39% of patients with lung cancer have COPD [22]. In the present study, the prevalence rate of COPD in patients with NSCLC was relatively higher than that previous study, possibly because it excluded patients with early lung cancer who have a shorter smoking history and comparatively good lung function. A comparison of the clinical characteristics between the COPD and non-COPD groups revealed that more patients in the COPD group were advanced in age, had a smoking history, and were diagnosed with squamous cell type, which is consistent with results of previous studies [23, 24]. A large number of comorbidities also occurred in the COPD group. Therefore, it can be inferred that patients with NSCLC and COPD had more respiratory symptoms and worse prognosis. Respiratory symptoms such as cough, sputum, and dyspnea were more frequent in patients with NSCLC and COPD than in those without, which supports the hypothesis and is consistent with the results of previous studies [25]. Declines in lung function and the severity of symptoms in patients with lung cancer are known to have significant effects on quality of life [26], and in particular, patients who suffer from dyspnea are known to be at higher risk of death and poor prognosis than those without dyspnea [6, 8]. Therefore, in this study, the quality of life in patients with advanced NSCLC was analyzed using the EORTC QLQ-C30 scale. No significant difference was found in the overall quality of life between the COPD and non-COPD groups. However, the COPD group had significantly reduced quality of life in certain aspects, such as the functional scale, cognitive and social functions, and some symptom scales, and the subgroup analysis results confirmed that overall quality of life decreased in the COPD group as the severity of airway obstruction increased. In particular, the difference was remarkable on the symptom scale related to dyspnea as well as the degree of decrease in social functioning. These results indicated that the severity of symptoms, including dyspnea, can affect various aspects of quality of life among patients with advanced NSCLC. Therefore, it is useful not only to collect baseline data regarding patient cancer status, but also to accurately evaluate patient symptoms, functional factors, presence of COPD, and severity of airway obstruction to present treatment directions for patient with lung cancer. Counselling for smoking cessation, prescription inhalers, pulmonary rehabilitation and other tailored management can improve functional status and relieve symptom burden of individual patients. Special attention by medical personnel is required.
This study also analyzed how COPD affected survival rates among patients with advanced NSCLC. Survival time was significantly shorter in the COPD group than that in the non-COPD group, which was a significant result in the univariate analysis, but not in the multivariate analysis corrected for the effects of other variables. This finding is similar to that of a previous study, which reported that the presence of COPD has no significant effect on prognosis for lung cancer patients [27]. This result suggests that it is difficult to determine the prognosis for patients with advanced NSCLC and COPD based on this single variable, because patients with COPD are more likely to have advanced stage, poor performance, and various complications during the treatment process.
This study had the following limitations. First, it was difficult to generalize the results because of the small sample size. However, the subjects were limited to patients with stage-3 and stage-4 NSCLC; those with stage-1, or stage-2 NSCLC were excluded, which had the effect of excluding other factors, such as curative surgery, that affects survival of patients. Therefore the subjects became homogeneous, which was an advantage, and the findings are highly relevant because they reveal how COPD affects symptoms, quality of life, and prognosis, even in patients with advanced lung cancer, unlike previous studies of long-term survivors after surgery [6]. Second, because the study had a retrospective design, its statistical power is rather weak. However, the questionnaire survey regarding symptoms and quality of life was done at the time of diagnosis, and objective lung functions were faithfully reflected, so the findings of this study are considered to be highly valuable for research. Third, the symptom questionnaire, pulmonary function from enrolled patients were recorded prospectively at the time of lung cancer diagnosis. Therefore, it was difficult to clearly identify the order of two diseases. However, COPD and lung cancer have a common etiology of smoking. And there are many opinions that COPD could be a driving factor in lung cancer by chronic systemic inflammation and DNA damage in time sequence [28]. We can suggest that patients with lung cancer and COPD at baseline develop more symptoms and lower quality of life than without COPD.