What are the causes of breast cancer and what are the measures needed to prevent it?

I wish we knew!: We really don't know what causes breast cancer. We do know that women with a long exposure to estrogen are at a higher risk. If you started your period early, or never got pregnant, you have more estrogen exposure. But these are things you can't really change. However, alcohol intake is associated with breast cancer, so decrease how much you drink. And lower your body fat. And avoid bpa plastics.