Breast cancer is due to cells mutating, and not all of these factors are something we want to change.
* age - breast cancer risk goes up with age, and we see a higher rate of breast cancer because it is occurring in women who didn't die of tuberculosis or in childbirth
* birth rate - the more children you have (and breastfeed), the lower the risk of breast cancer. The developed world has seen the number of childless women double and family size drop to 2 or fewer children per woman. I'm not going to advocate someone have a third child to lower the risk of breast cancer, and I won't tell someone to breastfeed due to the work it demands over bottle feeding - and I have done both with my children.
* abortion and miscarriage - the odds of breast cancer go up for every pre-term miscarriage and abortion a woman has; while I'd like both of these to go to zero, only reductions in miscarriage rates would be socially accepted
* obesity - this is a risk factor for breast cancer we can try to address individually and society wide
* family history - can't do much about this except genetic screening