Since you are interested in avoiding breast cancer I'll send you some links I dug up for someone who had breast cancer. (I regularly "spam" people with info like this. I feel so blessed to know stuff like this that I just have to share)
First: Bras cause breast cancer because they shut off the flow of blood to breast: http://www.all-natural.com/bras.html
Women who wore their bras 24 hours per day had a 3 out of 4 chance of developing breast cancer. Women who wore bras more than 12 hour per day but not to bed had a 1 out of 7 risk. Women who wore their bras less than 12 hours per day had a 1 out of 152 risk. Women who wore bras rarely or never had a 1 out of 168 chance of getting breast cancer. The overall difference between 24 hour wearing and not at all was a 125-fold difference.
Second: Milk has IGF-1, a hormone produced in the liver of the mother cow, which turns a little calf into a big cows in a few months, but when this hormone reaches breast and prostate cancer cells it causes them to grow rapidly too. (Despite my telling my mother and husband this, I can't get them to stop drinking milk arggg!)
On January 23, 1998 researchers at the Harvard Medical School released a major study providing conclusive evidence that IGF-1 is a potent risk factor for prostate cancer.
Should you be concerned? Yes, you certainly should, particularly if you drink milk produced in the United States.
This woman cured her breast cancer by eating raw food (it's a very inspirational story too):