Abstract 1742: Smoking and risk of mucinous epithelial ovarian cancer among 300,000 women
Authors: Licaj Idlir , Jacobsen Bjarne Koster , Selmer Randi Marie , Maskarinec Gertraud , Weiderpass Elisabete , Gram Inger Torhild 
Published: July 2016

Abstract
Background
In 2012, The International Agency for Research on Cancer classified mucinous epithelial ovarian cancer as tobacco related. In a recent pooled analysis of 51 epidemiological studies, smoking was associated with an increased risk of mucinous epithelial ovarian cancer, but not with other ovarian cancer histological subtypes. The main purpose of this study was to examine impact of smoking related increase in epithelial ovarian cancer according to histological subtypes and invasiveness in a large prospective cohort study.
Methods
We followed 300,398 Norwegian women born between 1899 and 1975, recruited from 1974 to 2003, by linkage to national virtually complete registries through December 2013. The three prospective cohort studies conducted by the Norwegian Institute of Public Health and included in the analysis were the Norwegian Counties Study (1974-1988), the 40 Years Study (1985-1999), and the Cohort of Norway (CONOR) Study (1994-2003). Their data were merged and analyzed altogether. We used Cox proportional hazard models to estimate hazard ratios (HR) and 95% confidence intervals (CI) for the association between smoking status, smoking-intensity and duration and epithelial ovarian cancer (EOC) histological subtypes. We used multivariable analyses stratified by birth cohort (≤1950&gt;) and cohort study, and tested for heterogeneity by BMI, attained education and physical activity.
Results
During &gt;5.9 million person-years, with a median follow-up of 19 years, 2,336 primary epithelial ovarian cancers (EOC) were identified, of which 1,647 (71%) invasive and 689 (29%) borderline. In our study, 38.0% of women were current, 21.1% former and 40.8% never smokers. Current versus never smokers risk of all histological subtypes of invasive EOC (multivariable HR = 0.97 95% CI, 0.86-1.08) was significantly different from the corresponding risk of all histological subtypes of borderline epithelial ovarian tumours (multivariate HR = 1.55 95% CI, 1.29-1.85) (pheterogeneity &lt; 0.0001). Compared with never smokers, current smokers had more than doubled risk of mucinous epithelial ovarian cancer (HR = 2.09 95% CI, 1.67-2.62). When stratified according invasiveness the corresponding figure was an increased risk of 78% [HR = 1.78 95% CI, 1.20-2.64 (ncases = 138)] for invasive mucinous epithelial ovarian cancer and more than doubled risk [HR = 2.26 95% CI, 1.71-2.97 (ncases = 302)] for borderline mucinous epithelial ovarian cancer (pheterogeneity = 0.34). Women who had smoked for more than 10 years had a 42% (HR = 1.42 95% CI, 1.07-1.88) increased risk of mucinous epithelial ovarian tumous compared to never smokers. The corresponding risk for those who smoked for longer than 20 years was increased with (HR = 2.13 95% CI, 1.68-2.70) (ptrend &lt; 0.001).
Conclusions
In this study smoking increases the risk of mucinous epithelial ovarian cancer in similar extent for invasive and borderline tumours.
Citation Format: Idlir Licaj, Bjarne Koster Jacobsen, Randi Marie Selmer, Gertraud Maskarinec, Elisabete Weiderpass, Inger Torhild Gram. Smoking and risk of mucinous epithelial ovarian cancer among 300,000 women. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1742.