Food Consumer - J. Luo of Mary Babb Randolph Cancer Center, West Virginia University in Morgantown, West Virginia and colleagues conducted the study and found that of women who had never smoked, those who had intensive passive smoking were almost 32 percent more likely to develop breast cancer, compared to those who were not exposed to passive smoking.

http://www.foodconsumer.org/newsite/Non-food/Lifestyle/passive_smoking_breast_cancer_1117120101.html