They have, but the link is not as strong with miscarriages; abortion really raises the risk.
Personal Observation: Every woman I know who has had breast cancer, also had either an abortion or multiple miscarriages when they were younger. (A sample of 5)
You know, I am a four-year survivor of stage three breast cancer and I have almost none of the risk factors: Had first child when young, breast fed both kids, never overweight, never had a miscarriage, etc, etc.
I also never had an abortion. Now I have to worry about whispers behind my back that perhaps I did. I hate that.