Age at first pregnancy is a factor in risk of breast cancer. Having your first birth at age 35 or older nearly doubles your risk; having your first birth younger than 20 cuts your risk down. With today's world where women get married later and delay childbirth for professional careers, this may be a factor in the rising risk of breast cancer we see.
It makes sense that a cohort of people who have abortions (usually young people) might have a higher risk than people who carried the pregnancy. Do people who don't get pregnant have the same risks as those who do, but terminate the pregnancy early? It may well not be the abortion causing the increased risk, but the lack of pregnancy at an early age.
Lifestyle choices we make clearly affect our risks of cancer, but we need to know more here before we can draw any easy conclusions.