Dear mrscat, In general it seems that the longer a women has reproductive levels of hormones, the more prone she is to breast cancer. If she menstruates for more than 40 years, she seems to have a particularly high risk. Early removal of the ovaries could reduce the risk of breast cancer. I cannot give you a percentage as many other factors also play into the risk equation. Early removal of the ovaries can increase your risk for osteoporosis. This would also start menopause for you so associated symptoms while your body adjusts to differing hormone levels can occur. Symptoms of menopause (such as hot flashes, vaginal dryness, or night sweats) vary between individuals. Use of hormone replacement therapy given your family history would most likely be avoided. You would want to discuss with your doctor these risks, things you can do to help prevent problems(i.e. calcium supplements) and focus on a healthy lifestyle (Healthy diet, exercise).