Breast Cancer Treatments and food sensitivities

I was just told that you cannot eat certain foods if you take certain drugs for cancer therapy, ie. you cannot use soy products or it can kill you.   This supposedly happened to the wife of a friend's brother.  I am vegetarian and use soy a lot.  Are there other foods that you cannot use?  What about the connection to this popular cancer drug and soy?  Where does one research this type of issue?  Thank you for any information.
LynneBrooke

[CCF-RN,MSN-JS]

Dear LynneBrooke:  The issue with soy is that it contains chemicals that are very similar to estrogens.  If the breast cancer is estrogen receptor positive, some of the treatments that are given work by blocking estrogen production.  By ingesting other estrogens, there is a theoretical concern that a person could be interfering with the therapeutic effect of reducing estrogen and, in fact, give the tumor the food it needs to grow.  It is not clear, however, that the types of plant estrogens found in soy and other foods are harmful to women being treated for breast cancer.  Oncologists vary in their opinions on this, but many do not restrict foods. Some do have concerns about dietary supplements that are not regulated by the FDA and may contain unknown amounts of estrogen-like substances.  Because these supplements do not require testing for safety or efficacy, it is unkown whether these might be helpful, harmful, or neutral.  You should discuss your specific situation with your oncologist and even a dietician at the center where you get your care so that you can learn safe ways of getting adequate nutrition that is appropriate for both your cancer situation and your vegetarian preferences.  

[Twocapes]

From what I've read and heard, you should not take excessive amounts of soy products if your tumor was estrogen positive.  The claim is that soy can produce estrogen in the body and you would be counter-acting the cancer drugs (Tamoxifen or Arimidex)that you are taking to elminate estrogen.  I have never heard of anyone dying from eating soy products.

[japdip]

Well I don't think it will kill you unless they meant that as the previous poster said ..... soy does act like Estrogen and if your tumor were ER+ it would be fed by Estrogen .... and there might be a possible recurrance which might in the long run "kill you". That's pretty far fetched when it comes to an explanation though. I personally do not intentionally injest soy products but I'm not a NUT about it. The same is said for Flax.

[Avidhiker]

I would run EVERYTHING by your oncologist.  Some recommend that you cease taking vitamins and minerals as they may also interfere with treatments, particularly chemo.  I just completed my chemo and now it's on to radiation, tamoxifen and Herceptin.  My opinion is that you do whatever it takes to treat this rotten disease even if it means altering your diet, dramatically or a little bit.

[carme]

ABSOLUTELY!!!