Smoking And Risk Of Lung Cancer, According To Cell Type By Gender In A Norwegian Cohort Of 600,000 Participants

Merethe HANSEN, UiT-The arctic university of Norway, Norway
BRAATEN T. 2 , LICAJ I. 1 , LANGHAMMER A. 3 , LE MARCHAND L. 4 , GRAM I. 1,6

1 Department of Community Medicine, Faculty of Health Sciences, The UiT Arctic University of Norway, Tromsoe, Norway
2 Department of Public Health and General Practice, Norwegian University of Science and Technology, Trondheim, Norway
3 Epidemiology Program, University of Hawaii Cancer Center, Honolulu, Hawaii, USA

Purpose
In Norway in 2013 lung cancer (LC) was the second most common cancer among men and the third most common cancer among women. Trends by histological type have shifted over time and in 2013 adenocarcinoma was the most frequent subtype, and squamous cell carcinoma ranked second. The purpose of the study was to examine by gender LC incidence overall and by subtype according to smoking history in a Norwegian prospective cohort.

Methods
We followed 585,583 Norwegian men and women born between 1897 and 1975, recruited from three different cohort studies conducted from 1974 to 2003, by linkage to national virtually complete registries through December 2013. We used Cox proportional hazards models to estimate hazard ratios (HR) and 95% confidence intervals for the association between ever versus never smoking status at enrolment and LC histological subtypes. We used multivariable analyses stratified by birth cohort and cohort study, and tested for heterogeneity by BMI, attained education and physical activity.

Results
During 11.6 million person-years, with a median follow up of 20 years, LC occurred in 3.714 men and 2.820 women. Among men 38% and 25% of the LC cases were adenocarcinoma and squamous cell carcinoma, respectively. For women the corresponding figures were 40% and 13%, respectively. Among men, ever smokers had an increased adenocarcinoma risk (HR= 6.93; 95% CI: 5.36-8.94), compared with never smokers. For women, this HR was 6.38 (95% CI: 5.25-7.76). For squamous cell carcinoma the HR was 35.16 (95% CI: 18.22-67.84) for men, and 37.94 (95% CI: 18.77-76.70) for women.
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Conclusions
Our findings suggest that, in Norway, adenocarcinoma is the most frequent LC cell type in both men and women, and that squamous cell carcinoma is more strongly associated with ever smoking in both sexes.
 
Funding: The project is supported by the Northern Norway Regional Health Authority.