Background:
Tobacco smoke is the most important human carcinogen and breast cancer is the leading cause of cancer among women, accounting in 2018 for nearly one in four of all female new cancer diagnoses worldwide, and around 15% of female cancer deaths. Numerous studies have been conducted to evaluate the association between smoking and breast cancer risk, with conflicting results. The last meta-analysis of all published studies reported significant 10% and 7% increases in breast cancer risk women exposed respectively to smoking and to second-hand smoke (SHS).

Objectives:
Aim of this work is to estimate the number of deaths and disability-adjusted life years (DALYs) from breast cancer attributable to smoking and SHS exposure in the European Union countries in 2017.

Methods:
The impact of smoking and SHS exposure on breast cancer was obtained through the comparative risk assessment method. Population attributable fractions (PAFs) were calculated by applying the relative risks of death from breast cancer to the Smoking Impact Ratio, for the burden from smoking, and to the prevalence of SHS exposure at home estimated from the Eurobarometer survey (allowing a 10-year lag-time) in the SHS burden estimation. The PAFs were then applied to the 2017 number of deaths DALYs estimated from the Global Burden of Disease study.

Results:
In 2017, 60,733 DALYs and 2,719 deaths from breast cancer could have been avoided by removing exposure to smoking in Europe Union. The proportion of DALYs from breast cancer lost respectively from smoking and SHS exposure was 2.2% and 0.4%, although geographically distributed with significant heterogeneity.

Conclusions:
These results are the first estimates of breast cancer burden in women attributable to smoking and SHS exposure for the Europe Union countries. It is important to widespread the link between smoking, SHS exposure and breast cancer, a relationship that is still little known.