Tobacco smoking is the major risk factor for lung cancer. However, approximately 10% of patients diagnosed with lung cancer have never smoked and knowledge of their characteristics and survival remain limited. Specific genetic alterations, e.g. ALK (anaplastic lymphoma kinase) rearrangements and EGFR (epidermal growth factor receptor) mutations, are more common in never-smoking lung cancer patients than in current or former smokers. We aimed to investigate characteristics of patients with different smoking history and estimate their lung cancer-specific survival.
This study was based on data from the Lung Cancer Database Sweden generated by record linkage between the Swedish National Lung Cancer Register and other population-based registers. Patients diagnosed with primary non-small cell lung cancer between 2002 and 2016 were included. The Kaplan-Meier method was used to estimate lung cancer-specific survival by smoking history (never-smokers, former smokers, and current smokers).
In total, 41,262 patients with lung cancer were included, of those 4,624 (11.2%) had never smoked. Never-smokers were older at time of the diagnosis (median: 73 years, Inter Quartile Range (IQR)=63-80) than current smokers (median: 67 years, IQR=61-73) and former smokers (median: 72 years, IQR=66-78). Women were overrepresented among never-smokers (66%) than among current (49%) and former smokers (43%). Adenocarcinoma was the most frequent histological subtype in all groups, but was proportionally more frequent in never-smokers (77%) compared to current smokers (52%) and former smokers (57%). The estimated overall (all stages) 2-year cause specific lung cancer survival was higher in never-smokers (35.9%, 95% CI 34.4 - 37.5) than among current smokers (29.4%, 95% CI 28.7 - 30.2) and former smokers (30.7%, 95% CI 30.0 -31.4).
The observed longer survival and the difference in histopathology suggest that tumours in never-smokers have a different pathogenesis and a different behaviour than tobacco-associated lung cancer. In further analyses, we will examine observed differences in outcomes in more detail, including the modifying role of other prognostic factors.
Clinical trial identification
Legal entity responsible for the study
Regional Oncologic Centre Uppsala-Örebro and Karolinska Institutet.
Has not received any funding.
All authors have declared no conflicts of interest.