Abstract 5058: The association between smoking status at diagnosis and breast cancer specific mortality in Ireland: A population based study

Background : Breast cancer is the most commonly diagnosed cancer worldwide and is a leading cause of breast cancer mortality in females. In recent years, 5 year survival rates have greatly improved for breast cancer however a clear disparity exists between survival in countries of high income compared to low and middle income. Disparity in survival also exists within individual countries. The identification of modifiable lifestyle factors can be an impactful and cost effective way to improve breast cancer outcomes worldwide, particularly in low income counties. An association between active smoking at diagnosis and breast cancer specific mortality has been reported by a number of studies to date. However, there is a paucity of studies undertaken in European populations. This large study was conducted to investigate whether smoking status at diagnosis is an independent prognostic factor for breast cancer specific mortality in the Irish female population. Methods : All data was derived from the National Cancer Registry Ireland database which records all incident cancers in the Republic of Ireland. Completeness of case ascertainment at 5 years after diagnosis is estimated to be at 98%. Multivariable Cox proportional Hazards models were used to compare breast cancer specific mortality in current smokers, ex-smokers and never smokers. Subgroup analyses by breast cancer molecular subtype was also conducted. Results : Data for women with known smoking status at time of diagnosis included 37,711 invasive breast cancer cases that accrued 263,626 women-years. Current smokers had a significantly increased risk of breast cancer specific mortality compared to never smokers (multi-variable HR, 1.3; 95% CI, 1.19, 1.41). Ex-smokers did not have a significantly different hazard ratio compared to never smokers (HR, 1.02; 95% CI, 0.92, 1.12). In subgroup analyses, risk of dying from breast cancer was increased most for current smokers with HER2+ disease compared to never smokers in the 5 years post diagnosis (HR, 1.53; 95% CI, 1.11, 2.12). This was followed by luminal A disease (HR, 1.39: 95% CI, 1.17, 1.65). Conclusion . Breast cancer patients who are current smokers at diagnosis have a statistically significant increased risk of breast cancer specific mortality. This risk differs depending on molecular subtype of disease. Citation Format: Maeve Kiely, Joesph McDevitt, Linda Sharp. The association between smoking status at diagnosis and breast cancer specific mortality in Ireland: A population based study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5058.