Abstract
Background
Cigarette smoking is one of the major causes of lung cancer. However, the correlation between smoking status and the survival of patients with lung cancer is uncertain. The present study aimed to evaluate the impact of smoking status on the mortality of patients with non-small cell lung cancer (NSCLC).
Methods
The medical records of 313 patients newly diagnosed with NSCLC between January 2005 and January 2006 were reviewed. Eligible patients were divided into ever-smokers (221 patients) and never-smokers (92 patients), and the overall survival and clinical characteristics of the two groups were compared. Predictors of survival were analyzed using Cox's proportional hazards regression.
Results
In ever-smokers, the mean age was higher, and male gender and squamous histology were predominant compared to never-smokers. The median survival time was longer in never-smokers (21.1 vs. 41.9 months, ever-smokers vs. never-smokers, respectively; P = 0.027). Overall survival estimates at 12, 24, and 60 months were 62.9 versus 82.6%, 43.4 versus 65.2%, and 31.2 versus 42.4%, in each group. Advanced age, advanced disease stage (stages III and IV), and coexistence of interstitial lung disease were analyzed as independent risk factors for shorter survival. Although ever-smoking was not an independent risk factor, current smoking was a risk factor for higher mortality.
Conclusions
The overall mortality of ever-smokers was higher than that of never-smokers in patients with newly diagnosed NSCLC, and current smoking was an independent risk factor for a poorer prognosis.
Keywords: Mortality, non-small cell lung cancer, risk factors, smoking
Introduction
Lung cancer accounted for 12.7% (1.61 million) of all new cancers in 2008 globally, and was the most common type associated with cancer-related deaths.1,2 Cigarette smoking is a well-established cause of lung and many other types of cancer, including cancers of the oral cavity, pharynx, larynx, esophagus, stomach, colon, liver, pancreas, cervix, kidney, and lower urinary tract.3,4 Both current and past smoking significantly increases the relative risk of lung cancer.4 Furthermore, millions of deaths worldwide as a result of cardiovascular disease, chronic obstructive lung disease, and lung cancer, are attributable to cigarette smoking.5
Although a causal relationship between smoking and the incidence of lung cancer is clear, there have only been a few studies on the impact of smoking status on the mortality of patients with lung cancer, and the results have not always agreed. Ferketich et al. reported that current smokers at the time of diagnosis with non-small cell lung cancer (NSCLC) had poorer survival rates compared to never-smokers, in a population of 4200 patients who participated in the National Comprehensive Cancer Network project in the United States.6 Nia et al. reported that non-smokers, former smokers, and recent quitters had better survival rates than current smokers in 311 surgical patients with NSCLC in Belgium.7 Conversely, the study by Meguid et al. showed no difference in the long-term survival of patients with NSCLC between current- and never-smokers.8
In the present retrospective study, long-term mortality and the clinical characteristics of patients with NSCLC were evaluated according to smoking status at the time of diagnosis. Additionally, risk factors for overall mortality in NSCLC patients were identified.
Methods
Data collection
Information concerning patients' baseline demographics and clinical characteristics was determined by reviewing the medical records of enrolled subjects. Age, gender, body mass index (BMI), smoking status, number of smoking pack-years, pulmonary function, Eastern Cooperative Oncology Group (ECOG) performance status, comorbidities, symptoms at presentation, tumor node metastasis (TNM) stage, histologic type of lung cancer, serum level of carcinoembryonic antigen (CEA), and method of treatment were obtained from medical records. Smoking status was categorized into: (i) never-smokers, patients who had never smoked or had smoked fewer than 100 cigarettes in their entire lifetime; (ii) former-smokers, patients who had smoked at least 100 cigarettes in their lifetime and had stopped smoking at least one month before the diagnosis of lung cancer; (iii) current-smokers, patients who continued smoking upon diagnosis or stopped smoking less than one month before the diagnosis of lung cancer and had smoked more than 100 cigarettes during their lifetime. The stage of lung cancer was graded according to the 7th American Joint Committee on Cancer TNM classification. NSCLC histologic type was divided into adenocarcinoma, squamous cell carcinoma, NSCLC not otherwise specified, and others, which included large cell carcinoma, carcinoid tumor, signet ring carcinoma, and mucoepidermoid carcinoma. Review of medical records also identified the date of death. If the date of death could not be identified from medical records, data from the Korean Ministry of Public Administration and Security on 26 October 2012 was used. Follow-up for survival analysis was defined as the time in months from diagnosis of lung cancer to the date of death or the date of the last outpatient visit.
Study population
In total, 313 patients aged over 20 years and newly diagnosed with NSCLC histologically and/or cytologically between January 2005 and January 2006 at Seoul National University Hospital, Seoul, Korea were enrolled in the current study. Among them, 221 (70.6%) patients were ever-smokers, and 92 (29.4%) patients were never-smokers. Subjects were excluded if they had a malignant disease other than lung cancer that affected their survival (n = 2), the lung cancer presented as an incidentally found ground-glass nodule (GGN) (n = 4), or smoking status could not be verified (n = 46). The Seoul National University Hospital Institutional Review Board approved the study (approval number IRB-H-1204-093-407). Eligible patients were divided into ever-smokers, including current and former smokers, and never-smokers. Demographic and clinical characteristics, as well as overall survival, were compared between the groups. Additionally, risk factors for mortality of NSCLC patients were analyzed.
Statistical analysis
Comparison of continuous variables, including age, BMI, number of smoking pack-years, pulmonary function, and serum CEA level, was performed by unpaired t-test between two groups or one-way analysis of variance (ANOVA) between three groups. Categorical variables, including gender, ECOG status, stage of lung cancer, histology, method of treatment, symptoms, and comorbidities were analyzed using Pearson's chi-squared test. The survival of patients was evaluated using Kaplan–Meier survival curves, and the difference was assessed by the log-rank test. The Cox proportional hazards model was used to estimate independent risk factors for the mortality of patients after adjusting for significant confounding factors. Variables with a P < 0.05 in a univariate analysis were entered into a multivariate analysis. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated. Differences were deemed to be statistically significant at P < 0.05. Statistical analyses were performed using SPSS version 18.0 for Windows (SPSS Inc., Chicago, IL, USA).
Results
Demographic and clinical characteristics
Ever-smokers were significantly older than never-smokers (mean ages, 64.7 and 57.6 years, respectively; P < 0.001). Male patients accounted for 96.8% of ever-smokers, in contrast to the 85.9% female predominance in never-smokers. The ratio of forced expiratory volume in 1 second (FEV1)/forced vital capacity (FVC) and predicted % of FEV1 were significantly lower in ever-smokers. About 67% of ever-smokers and 62% of never-smokers had stage III or IV disease. Interestingly, the proportion of patients with stage IV lung cancer was higher in never-smokers than in ever-smokers (46.7% vs. 32.1%, respectively). Squamous cell was the most common histologic type in ever-smokers, whereas adenocarcinoma was the most common histologic type in never-smokers. Surgical resection was the most commonly performed treatment in both groups, followed by chemotherapy. BMI, ECOG performance status, and serum CEA level were comparable in the two groups (Table 1).
Table 1.
Baseline characteristics of the study population
| Ever-smokers (n = 221) | ||||
|---|---|---|---|---|
| Current-smokers (n = 96) | Former-smokers (n = 125) | Never-smokers (n = 92) | P-value | |
| Age, year | 62.7 ± 8.5 | 66.2 ± 10.1 | 57.6 ± 10.4 | <0.001 |
| Male% / female% | 99.0/1.0 | 95.2/4.8 | 14.1/85.9 | <0.001 |
| BMI, kg/m2 | 22.1 ± 3.4 | 22.5 ± 3.0 | 23.0 ± 3.0 | 0.095 |
| Pack-years | 39.0 ± 15.8 | 39.0 ± 19.9 | 0 | <0.001 |
| FEV1/FVC, % | 66.1 ± 12.7 | 67.5 ± 11.7 | 79.1 ± 5.2 | <0.001 |
| FEV1, L | 2.1 ± 0.6 | 2.3 ± 0.7 | 2.1 ± 0.6 | 0.167 |
| FEV1, % | 77.3 ± 18.5 | 86.1 ± 22.2 | 96.9 ± 23.6 | <0.001 |
| FVC, L | 3.2 ± 0.8 | 3.3 ± 0.8 | 2.6 ± 0.8 | <0.001 |
| FVC, % | 82.8 ± 16.1 | 88.4 ± 15.9 | 89.8 ± 21.5 | 0.0127 |
| ECOG status | 0.692 | |||
| 0–1 | 91 (94.8) | 118 (94.4) | 88 (95.7) | |
| ≥2 | 5 (5.2) | 7 (5.6) | 4 (4.3) | |
| Stage | 0.001 | |||
| I | 18 (18.8) | 26 (20.8) | 27 (29.3) | |
| II | 13 (13.5) | 16 (12.8) | 8 (8.7) | |
| III | 35 (36.5) | 42 (33.6) | 14 (15.2) | |
| IV | 30 (31.3) | 41 (32.8) | 43 (46.7) | |
| Histology | <0.001 | |||
| Adenocarcinoma | 23 (24.0) | 46 (36.8) | 75 (81.5) | |
| Squamous cell | 47 (49.0) | 49 (39.2) | 2 (2.2) | |
| NSCLC, NOS | 18 (18.8) | 25 (20.0) | 12 (13.0) | |
| Others | 8 (8.3) | 5 (4.0) | 3 (3.3) | |
| Treatment | 0.039 | |||
| Surgery | 40 (41.7) | 52 (41.6) | 43 (46.7) | |
| Chemotherapy | 36 (37.5) | 42 (33.6) | 42 (45.7) | |
| Chemoradiation | 4 (4.2) | 8 (6.4) | 0 (0) | |
| Radiation | 5 (5.2) | 5 (4.0) | 2 (2.2) | |
| BSC | 7 (7.3) | 16 (12.8) | 4 (4.3) | |
| Unknown | 4 (4.2) | 2 (1.6) | 1 (1.1) | |
| Serum level of CEA, ng/ml | 20.6 ± 137.4 | 74.9 ± 436.1 | 25.4 ± 114.8 | 0.477 |
Values are presented as mean ± standard deviation or No. (%). P-values represent differences between ever- and never-smokers. BMI, body mass index; BSC, best supportive care; CEA, carcinoembryonic antigen; ECOG, Eastern Cooperative Oncology Group; FEV1forced expiratory volume in 1 second; FVC, forced vital capacity; NOS, not otherwise specified; NSCLC, non-small cell lung cancer.
Cough was the most common symptom at presentation in both groups. Sputum and dyspnea were significantly more common in ever-smokers than in never-smokers. The number of asymptomatic patients was greater in never-smokers (Table 2 ). Hypertension was the most common comorbid disease in both groups and was more common in ever-smokers (Table 2).
Table 2.
Symptoms at presentation and comorbidities of enrolled patients
| Ever-smokers (n = 221) | ||||
|---|---|---|---|---|
| Current-smokers (n = 96) | Former-smokers (n = 125) | Never-smokers (n = 92) | P-value | |
| Symptoms | ||||
| Cough | 42 (43.8) | 54 (43.2) | 37 (40.2) | 0.599 |
| Sputum | 33 (34.4) | 36 (28.8) | 17 (18.5) | 0.021 |
| Dyspnea | 13 (13.5) | 29 (23.2) | 19 (20.7) | 0.737 |
| Hemoptysis | 17 (17.7) | 26 (20.8) | 8 (8.7) | 0.019 |
| Weight loss | 8 (8.3) | 9 (7.2) | 4 (4.3) | 0.281 |
| Thoracic pain | 14 (14.6) | 11 (8.8) | 10 (10.9) | 0.910 |
| Extra-thoracic pain | 6 (6.3) | 4 (3.2) | 7 (7.6) | 0.273 |
| Hoarseness | 5 (5.2) | 3 (2.4) | 3 (3.3) | 0.875 |
| Neurologic symptom | 4 (4.2) | 3 (2.4) | 1 (1.1) | 0.288 |
| Others | 2 (2.1) | 2 (1.6) | 0 (0) | 0.194 |
| Asymptomatic | 19 (19.8) | 35 (28.0) | 34 (37.0) | 0.025 |
| Comorbidities | ||||
| COPD | 50 (52.1) | 61 (48.8) | 0 (0) | <0.001 |
| Hypertension | 17 (17.7) | 37 (29.6) | 13 (14.1) | 0.043 |
| Diabetes | 8 (8.3) | 21 (16.8) | 7 (7.6) | 0.164 |
| Cardiovascular disease | 6 (6.3) | 10 (8.0) | 2 (2.2) | 0.079 |
| Malignant disease | 4 (4.2) | 10 (8.0) | 9 (9.8) | 0.287 |
| ILD | 3 (3.1) | 6 (4.8) | 2 (2.2) | 0.406 |
| Others | 7 (7.3) | 7 (5.6) | 2 (2.2) | 0.128 |
| No comorbidities | 64 (66.7) | 60 (48.0) | 66 (71.7) | 0.010 |
Values are presented as No. (%). P-values represent for differences between ever- and never-smokers. COPD, chronic obstructive pulmonary disease; ILD, interstitial lung disease.
Comparison of survival between ever-smokers and never-smokers
Two hundred and twenty five out of 313 patients died and 88 patients survived during the study period. The median survival in the group of survivors was 84.0 months. The median survival time was 21.1 months in ever-smokers and 41.9 months in never-smokers (log-rank test; P = 0.027; Fig 1a). The median survivals for current and former smokers were 14.7 and 22.6 months, respectively. Kaplan-Meier survival estimates at 12, 24, and 60 months were 62.9 versus 82.6%, 43.4 versus 65.2%, and 31.2 versus 42.4%, in each group, respectively. Kaplan-Meier survival curves of current, former, and never-smokers are shown in Figure 1b.
Figure 1.
Overall survival of patients with non-small cell lung cancer (NSCLC) according to smoking status. (a) 
, ever-smokers; 
, never-smokers. (b) 
, current-smokers.; 
, former-smokers; 
, never-smokers.
Prognostic factors of survival in the study population
Univariate analysis showed that ever-smokers, advanced age, male gender, low BMI, advanced disease stage (stage III and IV), low FEV1 (% predicted), low FVC (% predicted), a high serum CEA level, ECOG ≥ 2, the presence of cough, sputum, dyspnea, extra-thoracic pain, hoarseness, and neurologic symptoms, and the coexistence of diabetes and interstitial lung disease (ILD) were predictors of high overall mortality. Advanced age, advanced disease stage (stage III and IV), and the coexistence of ILD were still significant predictors of high mortality after multivariate analysis (Table 3). Ever-smoking was a significant risk factor on univariate analysis, but ever-smokers had no increase in mortality over never-smokers after adjusting for covariates. Otherwise, current smoking remained a significant prognostic factor after multivariate analysis compared with current non-smoking, including former and never smoking (HR, 1.466; P = 0.032; Table 4).
Table 3.
Prognostic factors for higher overall mortality using univariate and multivariate analysis
| Univariate analysis | Multivariate analysis | |||||
|---|---|---|---|---|---|---|
| HR | 95% CI | p-value | HR | 95% CI | P-value | |
| Smoking status | ||||||
| Never-smokers | 1 | 1 | ||||
| Ever-smokers | 1.387 | 1.037–1.857 | 0.028 | 0.810 | 0.458–1.403 | 0.470 |
| Current-smokers | 1.499 | 1.067 | 0.020 | 1.050 | 0.576–1.916 | 0.873 |
| Former-smokers | 1.311 | 0.951–1.809 | 0.098 | 0.665 | 0.367–1.205 | 0.179 |
| Age, years | 1.036 | 1.022–1.050 | <0.001 | 1.044 | 1.026–1.061 | <0.001 |
| Gender | ||||||
| Female | 1 | 1 | ||||
| Male | 1.471 | 1.089–1.987 | 0.012 | 1.611 | 0.906–2.866 | 0.104 |
| BMI, kg/m2 | 0.944 | 0.904–0.986 | 0.009 | 0.957 | 0.912–1.005 | 0.076 |
| Stage | ||||||
| I | 1 | 1 | ||||
| II | 1.555 | 0.853–2.838 | 0.150 | 1.199 | 0.635–2.266 | 0.576 |
| III | 3.636 | 2.313–5.716 | <0.001 | 3.082 | 1.919–4.951 | <0.001 |
| IV | 7.594 | 4.889–11.794 | <0.001 | 7.573 | 4.654–12.323 | <0.001 |
| †Adenocarcinoma | 0.808 | 0.621–1.051 | 0.111 | |||
| ‡Squamous cell | 0.807 | 0.603–1.081 | 0.150 | |||
| FEV1, % | 0.984 | 0.978–0.990 | <0.001 | 0.991 | 0.976–1.006 | 0.224 |
| FVC, % | 0.981 | 0.974–0.989 | <0.001 | 1.004 | 0.987–1.020 | 0.676 |
| CEA, ng/ml | 1.001 | 1.000–1.001 | 0.008 | 1.000 | 1.000–1.001 | 0.165 |
| ECOG status | ||||||
| 0–1 | 1 | 1 | ||||
| ≥ 2 | 2.686 | 1.587–4.548 | <0.001 | 1.387 | 0.708–2.717 | 0.340 |
| Cough | 1.313 | 1.009–1.709 | 0.042 | 1.020 | 0.683–1.523 | 0.924 |
| Sputum | 1.424 | 1.069–1.896 | 0.01 | 0.850 | 0.555–1.302 | 0.455 |
| Dyspnea | 2.134 | 1.574–2.894 | <0.001 | 1.080 | 0.709–1.645 | 0.719 |
| Hemoptysis | 1.275 | 0.899–1.808 | 0.173 | |||
| Weight loss | 1.611 | 0.982–2.643 | 0.059 | |||
| Thoracic pain | 1.241 | 0.835–1.844 | 0.286 | |||
| Extra-thoracic pain | 2.013 | 1.191–3.405 | 0.009 | 1.737 | 0.958–3.151 | 0.069 |
| Hoarseness | 2.210 | 1.170–4.173 | 0.015 | 1.669 | 0.838–3.325 | 0.145 |
| Neurologic symptom | 3.669 | 1.795–7.500 | <0.001 | 2.216 | 0.925–5.309 | 0.074 |
| COPD | 1.371 | 1.046–1.797 | 0.022 | 0.985 | 0.590–1.647 | 0.955 |
| Hypertension | 1.162 | 0.854–1.581 | 0.341 | |||
| Diabetes | 1.575 | 1.078–2.303 | 0.019 | 1.079 | 0.702–1.658 | 0.729 |
| Cardiovascular disease | 1.319 | 0.768–2.267 | 0.316 | |||
| Malignant disease | 0.702 | 0.409–1.207 | 0.200 | |||
| ILD | 2.783 | 1.506–5.143 | 0.001 | 2.529 | 1.272–5.030 | 0.008 |
†Referent histology for adenocarcinoma is non-adenocarcinoma. ‡Referent histology for squamous cell is non-squamous cell carcinoma. CEA, carcinoembryonic antigen; CI, confidence interval; body mass index; COPD, chronic obstructive pulmonary disease; ECOG, Eastern Cooperative Oncology Group; FEV1forced expiratory volume in 1 second; FVC, forced vital capacity; HR, hazard ratio; ILD, interstitial lung disease.
Table 4.
Independent prognostic factors for higher mortality after multivariate analysis
| HR | 95% CI | P-value | |
|---|---|---|---|
| Smoking status | |||
| Current non-smoking | 1 | ||
| Current smoking | 1.466 | 1.034–2.079 | 0.032 |
| Age, years | 1.044 | 1.028–1.061 | <0.001 |
| Stage | |||
| I | 1 | ||
| II | 1.189 | 0.630–2.246 | 0.593 |
| III | 3.000 | 1.869–4.816 | <0.001 |
| IV | 8.149 | 4.980–13.334 | <0.001 |
| ILD | 2.591 | 1.306–5.138 | 0.006 |
CI, confidence interval; HR, hazard ratio; ILD, interstitial lung disease.
Discussion
The present study was conducted to evaluate the impact of smoking status at the time of diagnosis on the long-term overall survival of patients with NSCLC. The mortality of ever-smokers, including current and former smokers, was higher than that of never-smokers. After adjusting for confounding variables, ever-smoking was not an independent prognostic factor. Current smoking increased mortality compared to current non-smoking, including never and former smoking, even after adjustment. Ever-smokers were significantly older, predominantly male, and had a higher frequency of squamous cell histology, whereas never-smokers were younger, predominantly female, and had a higher frequency of adenocarcinoma.
It is well established that smoking is a major cause of mortality from diverse medical diseases.5,9,10 Of these, lung cancer is the third most common cause of death attributable to smoking (0.85 million deaths), with the highest fraction attributable to smoking (71%) in the year 2000.10 With respect to these deleterious impacts of smoking, there is a growing body of literature that evaluates the correlation between smoking and the survival of patients with lung cancer.
It seems obvious that smoking cessation improves the survival of patients with lung cancer.11–14 However, there is controversy concerning the impact of smoking status at the time of diagnosis on the survival of patients with lung cancer. The impact of smoking is usually assessed in terms of two aspects: (i) the difference in overall survival according to smoking status and (ii) the importance of smoking status as a prognostic factor after adjusting for confounders. The results of previous studies have varied widely. Nia et al. and Tammemagi et al. reported that current smokers had shorter survival rates than never- and former-smokers, and current smoking was an independent predictor of a poor prognosis.7,15 Similarly, in the recent report by Ferketich et al., current smokers had significantly poorer survival than never-smokers and current smoking was a poor prognostic factor.6 According to the report of Hanagiri et al., ever-smokers had worse survival than never-smokers; however, ever-smoking was not a prognostic factor in a multivariate analysis.16 In contrast, Toh et al. reported no difference in survival between ever-smokers and never-smokers; moreover, smoking status was not a significant prognostic factor.17 Furthermore, other reports found no survival difference between current and never smokers, and current smoking was not a significant prognostic factor.8,18 The results of the present study show overall poor survival among ever-smokers compared to never-smokers; however, ever-smoking did not have prognostic significance after adjusting for covariates. Current smoking, rather than ever-smoking, was an independent risk factor of a poor prognosis. Several reasons for these discrepancies exist. Among them, demographic differences in the study population, including ethnicity and stage of lung cancer, are important. The prognosis of surgical and non-surgical patients according to smoking status is expected to differ. In fact, most studies of surgical patients report a poor prognosis of smokers or smoking as a significant prognostic factor.7,16,19–21 Otherwise, studies that reported no impact of smoking included all stages of lung cancer, with more than 70% of patients with stage III or higher disease.8,17 The methods of determining and adjusting for various confounding factors also differed among the many studies.
Lung cancer in never-smokers accounts for about 10–15% of all cancers.22,23 Adenocarcinoma is the predominant histologic type, and females are more affected than males.24–27 In the present study, more than 80% of the subjects had the adenocarcinoma histological type, and females accounted for 85.9% of the never-smokers with lung cancer. Exposure to biomass or passive smoke may contribute to the high percentage of never-smoking women with adenocarcinoma. It is unclear why the proportion of never-smokers with stage IV disease was almost half of all never-smokers, and why never-smokers were significantly younger than ever-smokers in the present study population. We excluded lung cancer presenting as GGN, which was mostly adenocarcinoma in never-smokers, because the tumor biology is thought to be different in these cases. Despite the high proportion of patients with stage IV disease and the exclusion of GGN, the overall survival of never-smokers was significantly better.
Sputum was the only symptom more common at presentation in ever-smokers. Irrespective of other symptoms being comparable between the groups, never-smokers were significantly more asymptomatic. Considering this phenomenon, together with the advanced disease stage in never-smokers, a method of detecting asymptomatic lung cancer earlier in never-smokers is needed to improve the prognosis.
Lung cancer is a common comorbidity and a major cause of death in patients with chronic obstructive pulmonary disease (COPD).28,29 Among subjects in the present study, COPD coexisted with NSCLC in 35.5% of all enrolled patients and 50.2% of ever-smokers. The high incidence of COPD in ever-smokers is thought to be the reason for the predominance of male, lower FEV1 (% predicted), and a relative paucity of stage I disease and adenocarcinoma histology compared to never-smokers.
Previous studies of the impact of ILD on the survival of patients with lung cancer found that patients with both ILD and lung cancer had shorter overall survival rates than those without ILD. Furthermore, ILD was a significant predictor of a poor prognosis.30–32 In the present study, ILD was present in 11 patients (3.5%) at the time of diagnosis, and was a poor prognostic factor after multivariate analysis, as in previous reports. Thus, the presence of ILD should be considered an important factor at the time of diagnosis and treatment.
Limitations of this study are as follows: (i) the cause of death could not be identified, thus the cause specific mortality could not be evaluated because this is a retrospective study; (ii) the number of enrolled patients was relatively small as many patients with NSCLC were excluded because of unidentifiable smoking history; and (iii) a history of exposure to the passive cigarette smoke and biomass smoke could not investigated.
Conclusion
In conclusion, ever-smokers had poorer survival rates than never-smokers, and current smoking was a significant prognostic factor of a poor prognosis in the present study population. Further efforts towards smoking cessation are needed, not only to decrease the incidence of lung cancer, but also to increase the survival of patients with NSCLC.
Disclosures
No authors report any conflict of interest.
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