The American Cancer Society estimates the lifetime risk of a woman developing breast cancer is 13 percent or almost one in eight. In many cases, it's not known why a woman gets breast cancer. In fact, 75 percent of all women with breast cancer have no known risk factors. A risk factor is anything that makes it more likely you'll get a particular disease. But having one or even several risk factors doesn't necessarily mean you'll develop cancer. Most women with breast cancer have no known risk factors other than simply being women. Things that can increase your risk of breast cancer include:
Increasing age. Your risk of breast cancer increases as you age. Women older than 60 have a greater risk than do younger women.
A personal history of breast cancer. If you've had breast cancer in one breast, you have an increased risk of developing cancer in the other breast.
A family history of breast cancer. If you have a mother, sister or daughter with breast cancer, you have a greater chance of being diagnosed with breast cancer. Still, the majority of people diagnosed with breast cancer have no family history of the disease.
Inherited genes that increase cancer risk. Certain gene mutations that increase the risk of breast cancer can be passed from parents to children. The most common gene mutations are referred to as BRCA1 and BRCA2. These genes can greatly increase your risk of breast cancer and other cancers, but they don't make cancer inevitable.
Radiation exposure. If you received radiation treatments to your chest as a child or young adult, you're more likely to develop breast cancer later in life.
Obesity. Being overweight or obese increases your risk of breast cancer.
Beginning your period at a younger age. Beginning your period before age 12 increases your risk of breast cancer.
Beginning menopause at an older age. If you began menopause after age 55, you're more likely to develop breast cancer.
Having your first child at an older age. Women who give birth to their first child after age 35 may have an increased risk of breast cancer.
Postmenopausal hormone therapy.