It may be surprising to learn that most breast cancer is not determined solely by a girl’s genes or her family’s health history. According to the American Cancer Society, about 5-10% of breast cancer cases are thought to be gene defects (mutations) passed on from a parent and less than 15% of women with breast cancer have a family member with the disease.
Instead, scientists are learning that certain things in the environment – the air we breathe, the food we eat, the water we drink, and things we touch and put on our skin – may change the way a girl’s body develops as she grows, making her more vulnerable to developing breast cancer when she is an adult.
While risk factors for breast cancer may occur at any time over the course of a woman’s life, there are certain periods of time during which her body may be particularly sensitive to some of these risks, influencing her chance of developing breast cancer later in life. One such critical time is puberty (the time leading up to a girl’s first period).
Researchers have been learning more about how girls’ bodies mature. Also, they have been examining models of normal breast development and models of breast cancer in the laboratory to see which environmental exposures might lead to breast cancer.