I don't know that we get breast cancer because of any hormone 'imbalance'. I'm not saying that it's not accurate but I've never been told that by oncologists or my Ob-Gyn, or read it in any reliable studies, and have had hormone testing through the years. If a simple hormone imbalance were the triggering agent for breast cancer that could make the search for a cause a lot easier. And we could all be monitored for hormone balance annually as a safeguard. And insurers would happily cover it.

My impression is we get breast cancer because there's something causing breast cancer. One oncologist cited the fact that Japanese women, living in japan, have a far lower rate of breast cancer but, within a generation of moving to the United States, have the same elevated rate that we have. Clearly the women's genetics aren't modified by moving to the United States so something else is the causative variable.
Diet will be part of the answer but most first generation Japanese Americans do not modify their diets from what they ate in Japan so that leaves environmental and maybe food contaminants as a likely suspect but not yet proven as my guess.

I read a book by a female physician and Harvard professor who noted that the female body is designed to protect the fetus from toxicities and stores anything that it can't deal with, or excrete or rid the body of, in fat cells. That is, one job of fat cells is to store bad stuff and keep it out of the bloodstream. Her point was also that when dieting, or going through any kind of change of eating habits, that is critical to drink a lot of good-quality water and also pay attention to any symptoms of discomfort and monitor liver and kidney enzymes.

Since fat is a storage of contaminants as well as, as one doctor put it, an estrogen factory, fat plays a role in many cancers. (Which is alarming to read for someone, like me, who's been a lifelong serial dieter fighting against easy weight gain.)

So we have the biology for procreation and protecting offspring and the downside consequences of that if what I've read holds up.

At the same time, this argues that a change in diet that both increases nutrition, is weighted towards foods so far known to be antioxidants and natural anti-inflammatories, and losing some extra fat stores, seems like a strategy that can only do us good. And will likely boost immunity in myriad ways as well. As my brothers' doctors stressed when he was dealing with myriad health challenges, food is medicine.