Today my mother was diagnosed with breast cancer and her mother died from breast cancer. what are the chances of my sisters and i developing cancer?

That depends: You should get tested, all the women in your family... If you want to know more go here:.

C Genetic Counselor: Only 10-15% of breast cas are hereditary; your family history certainly raises the possibility, although it may still be coincidental. There is a simple blood test to identify the most common mutations (brca test). If your mom is brca (+), there is a 50% chance you could have inherited this as well. This is best sorted out w/a genetic counselor--your mom's cancer doctor can recommend one.