Is there any real evidence that soy estrogens cause estrogen dependent breast cancers to grow?

Question

My sister ate meat and she got breast cancer. I was a vegetarian for 20 plus years and I got breast cancer (I had fooled myself into thinking she got it from eating meat and that I was safe).We are now both in remission, but I went back to eating meat during chemo and now am trying to gradually get back...starting with soy milk. Anyone have any info?

I am asking about drinking soy milk and eating tofu and soy "meats" such as made by morningstar farms and soybean oil and soy sauce. Products such as those from soy beans but not soy estrogen pills or similar (I do not have hot flashes or any other problems to take estrogen pills for).I just want to be a vegetarian, if it is safe. I will ask my oncologist, too.

Answer 1

The results are basically mixted for this. Some studies find no stimulation of tumor growth, some studies do find a stimulation or at least maintainance of tumor size compared with a negative (no soy) control.

Here is one that do find stimualtion using both a genistein/isoflavone supplement and minimally processed soy molasses (used in Asia):

Carcinogenesis. 2004 Sep;25(9):1649-57

That other study (in the very same journal) seems to be contradicting it:

Carcinogenesis. 2006 Jul;27(7):1404-9.

As you see, this is still a hot debate. In our lab we have tested genistein (one of the guilty chemicals) at least once in vitro, and we have seen moderate tumor proliferation (like, a fraction of what you see using estradiol, your body's most powerful estrogen).

I've not read the studies in depht, only the abstract & conclusion. What could be questionned though is dosage. Genistein & isoflavones found in soy are relatively weak estrogens, and for a similar effect they must be taken in quite an amount.

So, basically I would advise at the very least against taking any kind of phytoestrogen supplement. Those are more likely, because of the sometimes high dose (which they need in order to have any kind of effect), to cause a ER+ tumor to grow.

As for soy milk, the stuff we get here is *probably* more processed than what is available in Asia. So we might hypothesize that the genistein/isoflavone contents would be lower. But unfortunately, the label on soy milk doesn't include the phytoestrogen contents... And in your case, your succeptibility to bc seems hereditary, so... I would use with moderation, especially if you are put on anti-estrogen therapy.

Answer 2

Estriol is approved for use outside the USA included for breast cancer survivors.
Natural USP Estrogen (Estriol) from wild yam has been tested in a study by the National Institute of Health on women (at half the dose prescribed outside the US) and their cells were examined under microscope. No evidence was found of abnormal growth.
In fact all the woman reported improvements using Estriol.
Shown to be safe and effective even for woman with cancer.
Problem is you can not buy Estriol in the US as Not FDA approved.
So most doctors probably never heard of it.

Answer 3

i also had a estrogen dependent breast ca almost 5 years ago. I was advised by my doctors to not take in anything like soy estrogen. I am currently taking tamoxifen for 5 years to avoid a recurrence, ask your doctors for advice on the soy products.

Good Luck to both of you