The association between smoking and the risk of pancreatic cancer - The Norwegian women and cancer (NOWAC) study

Abstract

Aims To examine the strength of association between cigarette smoking and the risk of pancreatic cancer in a cohort of Norwegian women. Methods A total of 149,243 women from Norwegian Women and Cancer Study were included in the statistical analysis. The participants were followed using the Cancer Registry of Norway and Norwegian Central Population Register till they were diagnosed with cancer, died or emigrated. The end of follow-up period was December, 2019. Age-adjusted and Multivariate adjusted Hazard Ratios with 95% CIs were obtained to examine the association between cigarette smoking and the risk of pancreatic cancer. Age at enrollment, education, BMI and physical activity were included as covariates in the final multivariate analysis. Results In age-adjusted and multivariate adjusted analysis, hazard ratios for pancreatic cancer in former smokers and current smokers were found to be higher than the reference category. Ever smokers had an overall 66% statistically significant increased risk of pancreatic cancer (HR = 1.66; CI = 1.34-2.06) as compared to never smokers. Former smokers had an overall 10% non-significant (HR = 1.10; 95% CI = 0.85-1.42), and current smokers had an overall 2-fold (HR = 2.39; 95% CI = 1.90-3.02) significant increased risk of pancreatic cancer, compared with never smokers. Higher age at the time of smoking initiation (>25 years), higher number of cigarettes smoked per day (>15) and higher number of total years of smoking (>30 years) were associated with 72% (HR = 1.72; CI = 1.11-2.67), 77% (HR = 1.77; CI = 1.26-2.48) and 89% (HR = 1.89; CI = 1.44-2.48) statistically significant increased risk of pancreatic cancer as compared to never smokers. iii Conclusion The findings of this thesis are in accordance with the previously published studies showing that ever smokers are at an increased risk of developing pancreatic cancer as compared to never-smokers. We also observed a dose-response relationship between the exposure and the outcome. Therefore, our findings are in support of a causal association between cigarette smoking and risk of pancreatic cancer. Keywords Cigarette smoking, pancreatic cancer, cox proportional, cohort, NOWAC study