The American Cancer Association cites many breast cancer risk factors which include:
Age: Increased risk as you age.
Menstrual periods: Women who had more menstrual periods because of starting at an earlier age and those having menopause at a later age are at higher risk.
Previous chest radiation: Women who had radiation therapy, especially as adolescents, when breasts are developing.
Diethylstilbestrol: This medication was used 1940-1960 with pregnant women to decrease the risk of miscarriage. Babies exposed to DES had higher incidence of breast cancer as adults.
Birth control: Women who take birth control seem to have a higher risk of breast cancer. This risk seems to go back down again as the women stop taking these medications.
Not having children: Women who did not have children or had their first child after age 30 have a higher risk of breast cancer.
Breastfeeding: This seems to have a protective effect in those who breast feed from 1 ½ – 2 years. This parameter is difficult to asses, however, in developed countries.
Alcohol: Drinking alcohol has been linked to risk of breast cancer.
Obesity: Being obese or overweight after menopause increases the risk of breast cancer.
Physical Activity: Exercise reduces the chances of cancer.