No, I know about childless women having a separate risk, it's a complex issue I agree. I know we're just talking semantics, but I would just make two points. Firstly, I think, as most scientists do, of something that increases your risk of cancer as being carcinogenic or oncogenic. Formula couldn't be considered to be either, particularly with respect to the women using it to feed their babies.
More importantly, most cancer causing factors (though not strictly all, I admit) have a dose response relationship, so the more you smoke the greater your chance of developing lung cancer and so on. The protective effect of breastfeeding does have a dose response relationship with breast cancer incidence- the more you bf, the greater the protection. The reverse can't possibly be true- whether you formula feed one baby or 10, the risk stays the same. That's why I would express it as a protective factor.
I was a breastfeeder, quite extended, and certainly don't want to row about it, I just think it's worth discussing