Cigarette smoking is a potential modifiable risk factor for breast cancer, which accounts for 30% of female cancer and is the second cause of cancer deaths in 2020.¹ However, there are limited studies and inconsistent results on the association between smoking and breast cancer with different estrogen receptor (ER) status.² In addition, the potential confoundings by alcohol use in observational studies may interfere with relation between smoking and breast cancer. ² Smoking is also genetically correlated with alcohol consumption.³