This is a retrospective analysis of 108 patients, who did HRCT and lung function tests, confirmed with lung cancer by pathology. The main findings of this study are: (1) Lung cancer patients with impaired lung function (PRISm or COPD) are more common in men. (2) Patients with impaired lung function are older than normal lung function patients. (3) Smoking is more familiar in people with impaired lung function. (4) The indexes of lung function (FEV1, FVC, FEV1/FVC) were decreased in PRISm group and COPD group. (5) Except for Ground-glass Opacities(GGO), other imaging appearances (bronchiectasis, bronchiectasis, thickened bronchial wall, pneumonectasis, atelectasis, interstitial inflammation) in PRISm group and COPD group were more than normal lung function group. (6) The numbers of patients in PRISm group with diameter measurements (IVCD > 2.1 cm, MPAD > 2.9 cm) were more than N-C group. The numbers of patients in COPD group with diameter measurements (AD > 3.9 cm) were more than N-C group. (7) In PRISm group and COPD group, lung cancer was found late, and the tumor volume was larger, mainly central squamous carcinoma. But the N-C group had the opposite results.

Despite recent advances, lung cancer is currently the main cause of cancer-associated mortality and the most common cancer all over the world [17]. The risk factors for lung cancer include tobacco consumption, airway lesions, genetic predisposition, air pollution and others [18]. Besides age (> 60 years), smoking status has been shown to have the greatest affect on the probability of developing lung carcinoma [19]. Lung carcinoma is one of the principal causes of hospitalization and death in patients with COPD [20]. Recent analysis of emphysema and airway obstruction in lung carcinoma screening group increased our understanding of COPD and lung cancer risk [21]. Spirometry was confirmed to play a significant role in COPD early diagnosis and screening [22]. On the basis of GOLD, COPD was confirmed in case of FEV1 to FVC ratio is less than 0.7, which means the patient breathes out below 70% of the air from lung in one second [23]. However one category of patients has been overlooked. Patients with preserved ratio impaired spirometry (PRISm) also has a low FEV1, exacerbations and symptoms. However, the forced vital capacity of those patients is also low, leading to a FEV1 to FVC ratio greater than 0.7. Some studies show that PRISm and COPD belong to lung function injury and PRISm is a precursor to COPD [24]. Therefore, we divided 108 lung cancer patients into three groups which respectively were lung cancer coexisting with normal lung function group, lung cancer coexisting with PRISm group, lung cancer coexisting with COPD group according to lung function in this study.

In the early diagnosis of lung carcinoma, HRCT plays an important role. Detection and screening of early lung cancer is very important to improve survival rates [25]. Imaging abnormalities and measures of chest CT imaging and pulmonary function measurement were included in this study in which we found that in contrast with N-C group, PRISm group and COPD group were predominantly male, older, smoked more, poorer lung function and had shorter survival time after diagnosis. There were more abnormal images in PRISm group and COPD group than in N-C group. In PRISm group and COPD group, lung cancer was found late, larger, and mainly central squamous carcinoma. But the N-C group had the opposite findings. We found that lung cancer in normal lung function group was discovered early, smaller, and mainly adenocarcinoma. Meanwhile the PRISm group and COPD group had significant poor survival rate compared with the normal lung function group. In addition, the survival rate of PRISm group was lower than that of COPD group. This discrepancy may be due to differences in smoking, air quality, co-morbid disease and so on. The N-C group often had stage I at first diagnosis, therefore had a higher rate of surgical resection and longer survival time. However, lung cancer was found late in the PRISm group and COPD group and was mostly stage IV at the time of first diagnosis. Therefore, patients with impaired lung function (PRISm and COPD) had lower surgical resection rate and shorter survival time.

Several limitations of our study should also be noted. First, it was a single-center retrospective study and thus the number of patients enrolled was limited. This raises a difficulty when overall survival in subgroups of lung cancer is compared and limits conclusions about differences between lung cancer groups. Second, the pulmonary function examination rate of lung cancer patients is low in clinical departments, resulting in the restriction of cohort sizes. Both of these limitations may be resolved by further analysis with larger cohort to acquire definite conclusions.