Below it are articles that that have cited this one subsequently.
Interesting. Here's the deal: A completed pregancy itself reduces the risk of breast cancer. If you compare nulliparous women (never gave birht) with parous women (have given birth) the risk of breast cancer is increased. The same is true for nulligravid women (never pregnant at all) with gravidity.
See this study here which matched gravdity and parity. That was in 2002, and subsequently appears to be accepted.
So, if you compare women who have had abortions with women who have not you have to match the two groups for parity and gravidity. If the group that has never had an abortion has a greater proportion of parous women, the numbers will be skewed, which appears to be the case in the study in the opening post.
"Breast cancer risk of parous women was unrelated to a history of miscarriage or induced abortion. Breast cancer risk was reduced among nulliparous women with a history of induced abortion relative to nulligravid women, although the risk estimate was imprecise. Risk declined as the number of induced abortions increased (P = 0.04). Our results do not support the hypothesis that induced abortion or miscarriage increase the breast cancer risk of young women."
So it looks like being pregant at all (and especially having a completed pregancy) reduces the risk of breast cancer. So, contrary to the OP, having been pregnant and having an induce abortion makes you less likely to develop breast CA than never having been pregnant at all. The study quoted was a case-control study that didn't appear to control enough.