It’s pretty obivious if you look at the charts of instances of breast cancers. They were much lower prior to about a decade after the birth control pills became widely used and they also jump again about a decade after abortion became legal.
Look at the chart of average weight of American women over the same period. It’s been climbing steadily, and additional body fat (even short of being medically classified as “overweight”) is well-known to increase estrogen levels and thus increase the incidence of breast cancer. There was an article just a day or two ago about the increasing incidence of breast cancer in young girls, even as young as 10. Increasing body fat (and the closely associated early onset of menstruation) is suspected as one of the factors in this alarming new trend. In addition, the rates of breast cancer in men have been significantly increasing for the past 25-30 years, and we can safely assume that this isn’t due to oral contraceptive use or abortion.