My question is this:
Is it the fact of having an abortion that raises the risk, or is it that women who have abortions are more likely to engage in other activities that might also raise the risk, such as taking birth control, smoking and drinking, and various other higher-risk activities as well?
It’s the massive hormonal buildup associated with pregnancy.
In a miscarriage, the hormones will tapper off naturally. In a completed pregnancy, the hormones build for a reason, and are again, lessened when no longer needed.
Abortion leaves a woman’s body, and especially the breasts “stuck” with a natural tumor “soup”.
Type 1 lobules, the most primitive and undifferentiated, are present in small girls. After first menstruation, some breast tissue develops into Type 2 lobules. These are more complex and include more ductules per lobule.
Type 1 and 2 lobules are where ductal cancers develop. The most cancer-resistant tissue, types 3 and 4 breast lobules, only develops during the third trimester of pregnancy.
Due to early pregnancy growth spurt during the first two trimesters, the woman who has an induced abortion is left with way more Types 1 and 2 lobules than she had before her pregnancy began. This leaves her with more places for cancer to start. By contrast, the woman who has a full term pregnancy is left with more mature, cancer-resistant Types 3 and 4 lobules than she had before her pregnancy began. This results in the protective effect of a full term pregnancy.
If her first pregnancy is full term, this will have a strong protective effect. Subsequent full-term pregnancies will have weaker, but still measurable protective effects.
The hormone induced physiological effect on the development of mammary gland tissue, that is triggered at the outset of impregnation, causes breast tissues to become more susceptible to cancerous growth if interrupted mid-course by an untimely and physiologically traumatic termination of the pregnancy. Abortion does not “cause” breast cancer. Rather, it renders breast tissue significantly more susceptible to developing cancer at some point, even years later.
I suspect that spontaneous abortion may produce a like effect, although perhaps, just perhaps, whatever triggers spontaneous abortion might also shut down the hormone moderated breast tissue modification process. (I am not a trained medical person; am only repeating, possibly imperfectly, what I have read from Dr. Brind and other experts).