Every 1 in 9 people (men and women) will develop breast cancer at some point in their lifetime. This is about 200,000 people per year. Researchers and scientists suspect up to 25% of these cancers are hereditary mutations on our genes.
Scientists are naming these genes BRCA (BReast CAncer) with a number afterward. They have been nicknamed "broken genes." The BRCA1 gene was the first one to be discovered. It is on the 17th chromosome. A second one, BRCA2, was discovered on the 13th chromosome. Right now BRCA1 & 2 are suspected for causing about 0.2 percent of hereditary breast and ovarian cancers. They are the current "leaders" in cause by their share of percentage. Scientists feel upward of 25% of all breast cancers are genetic in some way and they are on the verge of identifying a BRCA3, also on the 13th chromosome.
If you have a "broken gene" you are not guarenteed to develop cancer. Your risk is just higher than that of the general popular so doing monthly self-exams, getting annual mammograms and clinical checkups are very important to catching it early, getting treatment right way, and perhaps saving your life. You can take medication which will cut your risk in half.
If you have parents, siblings or aunts/uncles with breast cancer then you are considered at "high" risk of having a genetic predisposition to breast cancer. If one of your parents has breast cancer, then your risk is 50/50. If you or your spouse has hereditary breast cancer or carry a broken gene, then each of your children have a 50/50 risk of developing it.
There is a simple (for you) blood test to see if you have the BRCA1 or BRCA2 gene mutation. Ashkenazi (Eastern European) Jews are 10 times more likely than the general population to have these two hereditary mutuations. If there is breast or ovarian cancer in your family tree, pressure your doctor to order the test. My insurance covered the cost (in full) which is good because it's several thousand dollars. My results were negative.
Don't rule out the men for developing breast cancer (1% of all breast cancers are men) or passing down a broken gene. Every year about 2000 men develop breast cancer and 450 will die from it. The famous "Shaft" actor Richard Roundtree has breast cancer. See this link for more on him: http://abcnews.go.com/Health/OnCallPlusBreastCancerNews/story?id=4028791. There is also a website for men and breast cancer. See http://www.menstuff.org/issues/byissue/breastcancer.html.
National Institue of Health
National Human Genome Research Institute