These Risk Factors also affect a woman’s chance of having breast cancer, but can be changed or prevented: 

Estrogen  

Evidence suggests that the longer a woman is exposed to estrogen (estrogen made by the body, taken as a drug, or delivered by a patch), the more likely she is to develop breast cancer.
 

Late Childbearing   

Women who have their first child late (after about age 30) have a greater chance of developing breast cancer than women who have a child at a younger age.
 

Breast Density   

Breast cancers nearly always develop in lobular or ductal tissue (not fatty tissue). That's why cancer is more likely to occur in breasts that have a lot of lobular and ductal tissue (that is, dense tissue) than in breasts with a lot of fatty tissue. In addition, when breasts are dense, it is more difficult for doctors to see abnormal areas on a mammogram.
 

Radiation Therapy   

Women whose breasts were exposed to radiation during radiation therapy before age 30, especially those who were treated with radiation for Hodgkin's disease, are at an increased risk for developing breast cancer. Studies show that the younger a woman was when she received her treatment, the higher her risk for developing breast cancer later in life.
 

Weight   

Weight gain after age 18 is associated with an increased risk of post-menopausal breast cancer.
 

Physical Inactivity   

Indirect evidence exists indicating that there is an inverse relationship between amount of physical activity levels and one's risk of breast cancer.
 

Alcohol Consumption   

Some studies suggest a slightly higher risk of breast cancer among women who drink alcohol. The relationship between alcohol and breast cancer is consistent among associations of dietary factors and breast cancer risks, and is likely related to alcohol's (beer, wine, and liquor) ability to increase estrogen levels.