The American Cancer Society says:
The use of alcohol is clearly linked to an increased risk of developing breast cancer. The risk increases with the amount of alcohol consumed. Compared with non-drinkers, women who consume 1 alcoholic drink a day have a very small increase in risk. Those who have 2 to 5 drinks daily have about 1½ times the risk of women who drink no alcohol. Excessive alcohol use is also known to increase the risk of developing cancers of the mouth, throat, esophagus, and liver. The American Cancer Society recommends that women limit their consumption of alcohol to no more than one drink a day.
While the American Cancer Society refers to a "one drink a day" recommended limit on alcohol consumption, a pamphlet I have at home, from breastcancer.org, entitled "Your Guide to Reducing Your Risk of Breast Cancer" recommends limiting your alcohol intake to "fewer than 5 drinks a week."
If you want to know what you can do to reduce your breast cancer risk, limiting your alcohol is one place you can start.
For more information on reducing your risk for breast cancer, visit the American Cancer Society website or breastcancer.org.