Breast cancer happens when cells in the breast begin to grow abnormally, dividing uncontrollably and building up into a mass that usually is detected as a hard lump. But what causes that to happen? Experts still aren’t totally sure what exactly is the initial spark that triggers those cell mutations that cause breast cancer—but they do know that several risk factors up your chances.
Those risk factors can be broken down into two categories: lifestyle and genetic. “When we think about breast cancer, we try to break it down into things you can and can’t change,” says Megan Kruse, MD, an oncologist at the Cleveland Clinic in Ohio and assistant professor of medicine at the Cleveland Clinic Lerner College of Medicine. “There are risk factors you’re born with and then there are others that you can actually do something about.”
Know this: Just because you have one or more breast cancer risk factors, that doesn’t necessarily mean you’ll get it. And on the flip side, even if you have none of the following risk factors, that doesn’t mean you’re 100 percent in the clear (though knowing them can help you in your efforts to prevent breast cancer). All that said, here are the biggest breast cancer risk factors to know.
Drinking alcohol
Even a few drinks a week is linked with an increased risk of breast cancer in women. According to the American Cancer Society, women who drink two or three drinks a day have a 20 percent higher risk of developing breast cancer compared to women who don’t drink alcohol. Alcohol can raise estrogen levels in the body, which may be why it increases your risk.
Being overweight or obese
“Obesity is a risk factor particularly among postmenopausal women,” says Dr. Kruse. Before menopause, your ovaries make most of your estrogen; after menopause, the ovaries stop making estrogen so most of the hormone comes from fat tissue—having too much fat can raise estrogen levels and increase your risk of getting breast cancer. Additionally, women who are overweight tend to have higher blood insulin levels, which have been linked to breast cancer. “The closer a woman is to her ideal body weight, the less risk she has of getting breast cancer,” notes Dr. Kruse.
Not exercising
Evidence is growing that regular physical activity reduces breast cancer risk, especially in women past menopause. Though how much activity you need is unclear, some studies have found that even just a few hours a week of exercise may be helpful (though more is likely better).
Having kids later in life
“We see a slightly increased risk of breast cancer among women who have either never had a child or had their children after the age of 30,” says Dr. Kruse. That said, the effect of pregnancy seems to depend on the type of breast cancer you have. For example, having a type of breast cancer called triple-negative seems to increase risk.
Not breastfeeding
Some studies suggest that breastfeeding may slightly lower breast cancer risk, especially if it’s done for one and half to two years. This may be because breastfeeding reduces a woman’s total number of lifetime menstrual cycles.
Taking hormonal birth control
The hormones in some in birth control methods including oral contraceptives, birth control shots, and IUDs may increase breast cancer risk.
Using hormone therapy after menopause
Hormone therapy with estrogen and progesterone may help relieve symptoms of menopause and help prevent osteoporosis, but it can also increase the risk of developing and dying from breast cancer. It can also increase the likelihood that the cancer is found at a more advanced stage and up the risk of heart disease, blood clots, and strokes. According to the American Cancer Society, the risks may outweigh the benefits of hormone therapy so be sure to talk to your doctor before using it.
Being a woman
Since breast cancer is a hormonally-driven cancer—it typically needs estrogen in order to grow—simply being a woman is probably the biggest risk factor for developing breast cancer, says Jennifer Specht, MD, an oncologist at Seattle Cancer Care Alliance and an associate member of the clinical research division at Fred Hutchinson Cancer Research Center.
Getting older
The risk of breast cancer increases with age. Most breast cancers are found in women age 55 and older.
Having certain inherited genes
About 5 to 10 percent of breast cancer cases are thought to be hereditary, meaning they are the result of gene defects (called mutations) passed on from a parent. Specifically, having an inherited mutation of the BRCA1 or BRCA2 gene is the most common cause of hereditary breast cancer.
Having a family history of breast cancer
The American Cancer Society stresses that most women (about 8 out of 10) who get breast cancer do not have a family history of the disease. However, having a first-degree relative (mother, sister, or daughter) with breast cancer almost doubles your risk, and having two first-degree relatives triples your risk. Overall, less than 15 percent of women with breast cancer have a family member with the disease.
Having breast cancer in the past
If you’ve had cancer in one breast, you have a higher risk of developing a new cancer in the other breast or in another part of the same breast. Although the risk is low, it tends to be higher for younger women with breast cancer.
Your race and ethnicity
White women are slightly more likely to develop breast cancer than African-American women; however, breast cancer is more common in African-American women under the age of 45, and African-American women are more likely to die from breast cancer at any age. Asian, Hispanic, and Native American women have both a lower risk of developing and dying from breast cancer.
Dense breast tissue
Breasts are made up of fatty tissue, fibrous tissue, and glandular tissue. You might be told you have “dense breasts” if a mammogram shows you have more glandular and fibrous tissue and less fatty tissue. Women with dense breasts are 1.5 to 2 times more likely to develop breast cancer than women with average breast density, according to the American Cancer Society.
Getting your period early
If you got your period before the age of 12, that means you’ve experienced more menstrual cycles in your lifetime and have been more exposed to estrogen and progesterone, which increase the risk of breast cancer.
Going through menopause after 55
Conversely, going through menopause after age 55 means you’ve had more menstrual cycles which again prolongs your exposure to estrogen and progesterone, increasing your risk.
Having radiation to your chest as a kid
“Being treated for a childhood cancer with radiation to the chest significantly increases the risk of developing breast cancer later in life,” says Dr. Specht. The risk is highest if you had radiation as a teen or young adult when your breasts were still developing.
Exposure to DES
Women who took diethylstilbestrol (DES), an estrogen-like drug administered from the 1940s through the early 1970s to lower the chances of miscarriage, have a slightly increased risk of developing breast cancer.
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