Menstrual periods

Menstrual periods

Women who have had more menstrual cycles because they started menstruating early
(before age 12) and/or went through menopause later (after age 55) have a slightly higher
risk of breast cancer. The increase in risk may be due to a longer lifetime exposure to the
hormones estrogen and progesterone.
Previous chest radiation
Women who, as children or young adults, had radiation therapy to the chest area as
treatment for another cancer (such as Hodgkin disease or non-Hodgkin lymphoma) have
a significantly increased risk for breast cancer. This varies with the patient's age when
they had radiation. If chemotherapy was also given, it may have stopped ovarian
hormone production for some time, lowering the risk. The risk of developing breast
cancer from chest radiation is highest if the radiation was given during adolescence, when
the breasts were still developing. Radiation treatment after age 40 does not seem to
increase breast cancer risk.
Diethylstilbestrol exposure
From the 1940s through the 1960s some pregnant women were given the drug
diethylstilbestrol (DES) because it was thought to lower their chances of miscarriage
(losing the baby). These women have a slightly increased risk of developing breast
cancer. Women whose mothers took DES during pregnancy may also have a slightly
higher risk of breast cancer. For more information on DES see our document, DES
Exposure: Questions and Answers.
Lifestyle-related factors and breast cancer risk
Having children
Women who have had no children or who had their first child after age 30 have a slightly
higher breast cancer risk. Having many pregnancies and becoming pregnant at a young
age reduce breast cancer risk. Pregnancy reduces a woman's total number of lifetime
menstrual cycles, which may be the reason for this effect.