A study has found that greater levels of drinking before a first pregnancy raise the risk of the disease.
Women who never have children, or delay becoming pregnant, were already known to be more susceptible to breast cancer.
The research, based on findings from 91,000 women aged 15 to 40, found a link with alcohol intake between the start of menstrual periods and first pregnancy.
A woman's breast tissue is thought to be sensitive to cancer triggers in this time.
Alcohol consumption between menarche - or first period - and first pregnancy also raised the risk of benign breast disease. In both cases, the more women drank the higher their risk of contracting the disease.
Writing in the Journal of the National Cancer Institute, the researchers led by Dr Ying Liu from Washington University School of Medicine in St Louis, US, said: "The longer the duration of menarche (first period) to first pregnancy, the higher is a woman's risk of breast cancer."
Every 10 gram per day increase in alcohol consumption raised the risk of breast cancer by 11%.