Breast Cancer: Causes and Risk Factors

Early screening and prevention measures can lower your risk of breast cancer and, when caught early, doctors can cure many breast cancer types with treatment. Knowing which breast cancer risk factors you might have can help make screening more effective.

There isn’t one specific cause of breast cancer, but there are some factors that can increase your risk of diagnosis, including weight, age, and gender. A family history of breast cancer or a genetic mutation can also be strong risk factors for the disease.

There are a number of risk factors for breast cancer. There are some that you’re able to control through lifestyle changes, but others cannot be altered.

Preventable Risk Factors

Over the years, experts have discovered activities, medications, and other factors that may increase your risk of developing breast cancer.

• Weight: Women who are overweight after menopause may have an increased risk of breast cancer.

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  After menopause, the main source of estrogen in the body is fat tissue.

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  High estrogen has been linked to breast cancer, and so an increase in body fat can increase risk.

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• Inactive lifestyle: Though experts aren’t sure why, regular exercise seems to reduce breast cancer risk, especially in post-menopausal women. The connection isn’t fully clear, but the lowered risk could be due to weight loss, lower inflammation, and hormone changes caused by exercise.

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• Hormone supplements: Doctors may prescribe estrogen, sometimes combined with another hormone called progesterone, to treat symptoms of menopause. Some studies show hormone therapy may increase your risk of breast cancer.

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• Birth control: Birth control pills have been associated with a slightly higher risk of breast cancer. Oral birth control methods use hormones, which may increase breast cancer risk Your risk goes down 10 years after you stop taking the pills. Although only a few studies have measured the risk from birth control implants, patches, and rings, they may also increase your risk.

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• Breastfeeding: Choosing not to breastfeed may increase your risk of breast cancer, while breastfeeding for a year or more may decrease risk, according to a 2022 study.

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  Although studies in the United States are lacking in this area, experts think the slightly lower risk may be related to fewer lifetime menstrual cycles.

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• Alcohol: Breast cancer risk can go up with any amount of alcohol consumption.

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  One large study review found that for every 10 grams (g) of pure alcohol consumed per day, the risk of breast cancer increased by 5 percent for premenopausal women and 9 percent after menopause.

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  For context, you get 14 g of pure alcohol in a can of standard 5 percent beer or a glass of table wine.

Unpreventable Risk Factors

This group of breast cancer risk factors comes from genetics, health history, age, and race. While you cannot change these risk factors, knowing which ones you have can help you and your healthcare provider make a plan for screening so you can catch the cancer early.

• Sex at birth: Being born female is the highest unpreventable risk factor for breast cancer. While males can also develop breast cancer, they account for less than 1 percent of all new cases.

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• Age: As women age, their risk of breast cancer increases. For example, a 30-year-old woman’s chance of developing breast cancer before she turns 40 is about 1 in 200, whereas a 70-year-old woman’s 10-year risk is 1 in 25.

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• Height: A few studies have shown a link between being taller and a higher risk of breast cancer. Though experts aren’t sure exactly why, they think the connection could be related to nutrition in early life, and genetic and hormonal factors.

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• Reproductive history: If you had your first menstrual period before age 12 or began menopause after age 55, the increased exposure to hormones like estrogen may raise your risk of breast cancer. More periods during your life means more estrogen exposure, which increases your breast cancer risk.

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• Pregnancy: While breast cancer risk rises for 10 years after the birth of your first child, pregnancy after the age of 30 or no history of pregnancy may also increase your risk because of a higher number of menstrual periods and exposure to more estrogen.

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• Dense breasts: Some women have greater breast density than others, and this arrangement of tissue can make tumors difficult to identify on a mammogram You may have dense breasts if you are pregnant, breastfeeding, taking hormone supplements, or are younger. A higher breast density can also be genetic.

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• Personal history: Women have a higher risk of breast cancer diagnosis if they’ve already had breast cancer or certain noncancerous breast diseases — like atypical ductal hyperplasia or lobular carcinoma in situ.

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• Previous treatment: Radiation therapy to the chest or breast areas before the age of 30 increases a person's risk of developing breast cancer later on. This therapy uses high doses of radiation to kill cancer cells, but it can also affect nearby healthy cells.

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• Race and ethnicity: Non-Hispanic white women are more likely to receive a breast cancer diagnosis than Black women, but in women under the age of 45, the reverse is true. Black women are more likely to die of breast cancer than white women, no matter their age. Asian, Hispanic, and Native American women have a lower risk than these two groups.

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Inherited Breast Cancer and Gene Mutations

• Family history: The risk of breast cancer increases if certain family members have had breast or ovarian cancer. If a first-degree relative — a mother, sister, or daughter — has one of these cancers, the risk nearly doubles.
• Genetics: Some mutations to genes, like BRCA1 and BRCA2, can put women at a higher risk of breast cancer. Around 5 to 10 percent of breast cancers can be linked to these mutations.

Whether your risk factors are preventable or not, you can take steps to reduce your chances of developing breast cancer.

Through testing, counseling, and lifestyle changes, you can advocate for yourself and take charge of your breast cancer care.

• Genetic testing and counseling: A good first step in breast cancer prevention is to make an appointment with your healthcare provider. They can talk to you about your risk factors and test for the BRCA1 and BRCA2 gene mutations.
• Breast cancer screening: Recommendations vary depending on your risk of breast cancer, with screening beginning at the age of 40 for some people. Women over 55 may switch to getting a mammogram every other year or continue with annual mammograms.

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• Regular exercise: The ACS recommends all adults try for 150 to 300 minutes of moderate-intensity exercise, or 75 to 150 minutes of vigorous exercise, each week for optimal breast cancer prevention. The daily amount can vary, as long as you get the weekly total in.

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• Healthy weight: The more fat cells you have, the more estrogen has access to your system, which can increase your risk of diagnosis. As much as you can, stay at a healthy weight to reduce that risk.
• Limited alcohol consumption: The ACS recommends cutting out alcohol completely, though this may not be doable for everyone. If you do decide to drink, try not to have more than one drink per day.

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• Breastfeeding: If done for over a year, breastfeeding decreases your risk of a breast cancer diagnosis.

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You can also use a Breast Cancer Risk Assessment Tool provided by the National Cancer Institute to estimate your breast cancer risk. While this tool does not replace your provider’s assessment and can’t check for gene mutations, it can give you some idea of your risk level.

If your healthcare provider has confirmed that your breast cancer risk is high — whether from gene mutations, family history, or a large number of risk factors — you have some options beyond lifestyle changes.

Close Observation

If your risk is high, your provider may suggest close monitoring for signs of early breast cancer. Have a discussion with your provider regarding when you should start breast cancer screening and if you need additional imaging, such as a breast ultrasound or MRI.

Medications

Some medications can lower your risk of breast cancer, including:

• Anastrozole (Arimidex)
• Exemestane (Aromasin)
• Raloxifene (Evista)
• Tamoxifen (Nolvadex)

Preventive (Prophylactic) Surgery

For those at extremely high-risk for breast cancer, such as women who carry the BRCA1 or BRCA2 gene mutation, a preventive mastectomy is an option. This surgical procedure removes both breasts before cancer can begin to grow.

Another surgical option is an oophorectomy — a surgery to remove your ovaries and fallopian tubes. Your ovaries are the main producers of estrogen in the body, and so their removal may reduce risk.

There are some risk factors for breast cancer that you can prevent with lifestyle adjustments and others that you cannot. Being aware of any breast cancer risk factors you have can make screening more effective and make it easier to find and treat breast cancer early.