Breast cancer is the second most common cancer in the United States, striking 1 in 8 women.

Research shows that diet, smoking, and other lifestyle factors play roles, but it remains unclear what exactly causes the gene mutations that lead to breast cancer. As scientists work on unraveling that mystery, great strides are being made in prevention, precision medicine, and targeted gene therapies that combat the fast-growing tumor cells and reduce recurrence.

"We're continually researching ways to identify who is most vulnerable," says Dr. Reva Basho, breast medical oncologist at Cedars-Sinai.  "We're not yet sure why healthy young women sometimes develop breast cancer. But we do know that the best prevention is for women over 40 to have annual mammograms, and for younger women to administer self-exams."

Below are 7 of the most common risk factors for breast cancer, but there are others. The best way to assess your individual risk is to talk to your doctor.

Family history
A family history of breast cancer increases the likelihood of developing abnormalities. If your mother, sister, or an aunt had breast cancer before age 50, talk to your doctor about proactive monitoring and mammograms.

BRCA Gene Mutation
Some 20-25% of hereditary breast cancers are attributed to BRCA1 or BRCA2 gene mutations, although not everyone with the gene will get breast cancer. The gene mutations inhibit the production of tumor suppressor proteins that aid in cell repair. Notably, BRCA mutations raise the risk of developing cancer at a young age. BRCA1 and BRCA2 mutations have also been associated with ovarian cancer and other cancers.

Ethnicity
Men and women of Ashkenazi Jewish ancestry are 10 times more likely to carry a BRCA mutation.

Weight
Among postmenopausal women, obesity increases the risk of breast cancer by 20-40%.

Mammographic Breast Density
The term breast density refers to fibrous breast tissue that makes it harder to detect cancerous tumors on a mammogram. If you receive a diagnosis of dense breast tissue, discuss alternative screening methods with your doctor.

Radiation therapy
Radiation therapy to the chest before age 30 increases the risk of developing breast cancer later in life.

Smoking
By now most people are aware of the negative effects of smoking, one of the most preventable causes of death. However, studies show that when you start smoking matters too. If you began in your teens, your risk of breast cancer is higher, even if you quit later in life.