Causes and Risk Factors for Breast Cancer

Breast cancer develops when genetic mutations disrupt the normal life cycle of breast cells, causing them to grow and divide uncontrollably. While the exact cause is often unknown, researchers believe that a combination of genetic, hormonal, lifestyle and environmental factors may contribute to its development.

According to the American Cancer Society, approximately 1 in 8 women in the United States will develop invasive breast cancer during their lifetime. Although the condition primarily affects women, it can also occur in men. Understanding the factors that may increase breast cancer risk and the importance of early detection can help support better outcomes.

What causes breast cancer?

Breast cancer begins when cells in the breast acquire DNA damage that interferes with their normal growth and repair processes. As these abnormal cells continue to multiply, they can accumulate, form a tumor and potentially spread to nearby lymph nodes or other parts of the body.

Researchers have identified several factors that may contribute to DNA damage in breast cells, increasing the likelihood of abnormal cell growth and breast cancer development. These include:

• Inherited gene mutations – Some people inherit harmful mutations in certain genes, such as breast cancer gene 1 (BRCA1), breast cancer gene 2 (BRCA2) or partner and localizer of BRCA2 (PALB2), which increase the risk of breast cancer. These genetic changes are passed from parent to child.
• Acquired gene mutations – Most breast cancers are associated with genetic changes that occur during a person’s lifetime rather than being inherited. These mutations can disrupt normal cell growth and repair mechanisms, allowing abnormal cells to survive and multiply.
• Age-related DNA damage – Over time, breast cells naturally accumulate DNA damage from normal cellular processes and environmental exposures. This cumulative damage may lead to the development of cancer-causing gene mutations.
• Hormonal influences – Estrogen and progesterone help regulate breast development and function. Prolonged exposure to these hormones may increase the likelihood of developing certain types of breast cancer.
• Environmental exposures – Researchers continue to investigate how ionizing radiation and other environmental factors may contribute to DNA damage and breast cancer development.

What are the risk factors for breast cancer? 

Anyone can develop breast cancer, but certain factors may increase the risk. Some risk factors are related to lifestyle and can be controlled to a certain extent, while others cannot.

Risk factors for breast cancer include:

• Older age – The risk of breast cancer rises with age, with most cases diagnosed in adults older than 50.
• Female sex – Breast cancer occurs far more often in women than in men, primarily due to differences in breast tissue and hormone exposure.
• Personal history of breast cancer – Individuals who have had breast cancer previously face an increased risk of developing a new breast cancer in the future.
• Family history of breast cancer – Having a close relative with breast cancer may increase risk, particularly if multiple family members have been diagnosed.
• Dense breast tissue – Women with dense breasts, which contain more fibrous and glandular tissue than fatty tissue, may have a higher risk of developing breast cancer. Dense tissue can also make tumors more difficult to detect on mammograms because both appear white on imaging.
• Prolonged estrogen exposure – Early menstruation (before age 12), late menopause (after age 55) or the use of combination or estrogen-only hormone replacement therapy (HRT) can increase lifetime estrogen exposure and breast cancer risk.
• Excess body weight – Being overweight or obese, particularly after menopause, can increase breast cancer risk. Fatty tissue produces estrogen, which may promote the growth of some breast cancers.
• Physical inactivity – A sedentary lifestyle is associated with an increased risk of breast cancer. Researchers believe that physical activity may help reduce risk by regulating hormone levels, limiting weight gain and improving overall metabolic health.
• Alcohol use – Studies have consistently linked alcohol consumption to an increased risk of breast cancer. Even moderate drinking may raise the risk, which appears to increase with the amount of alcohol consumed.
• Prior radiation exposure – Radiation therapy delivered to the chest, particularly at a young age, can increase the risk of breast cancer later in life.
• Inherited genetic mutations – Certain hereditary gene mutations, including BRCA1, BRCA2 and PALB2 mutations, can significantly increase breast cancer risk.

Dense breast tissue increases a patient’s risk of developing breast cancer but also makes it harder to find the breast cancer on a mammogram.

Bethany Niell, MD, PhD

Which risk factors for breast cancer are modifiable (factors you can control)?

Some breast cancer risk factors are related to lifestyle choices and may be reduced through healthy behaviors and informed health care decisions. While risk management cannot prevent breast cancer in every case, it may help lower the likelihood of developing the condition.

Modifiable risk factors for breast cancer include:

• Alcohol consumption – Consuming alcoholic beverages is associated with an increased risk of breast cancer. Limiting or avoiding alcohol may help reduce the risk.
• Excess body weight – Achieving and maintaining a healthy body weight, especially after menopause, may help lower breast cancer risk.
• Physical inactivity – Regular exercise may help lower breast cancer risk by supporting healthy hormone levels, reducing inflammation and helping maintain a healthy body weight.
• Certain hormone therapies – Long-term use of combined hormone replacement therapy after menopause may increase breast cancer risk for some women. Anyone considering HRT should discuss the potential benefits and risks with their physician.
• Smoking – Research suggests that tobacco use may increase breast cancer risk, particularly among women who began smoking at a young age or who have smoked for many years.

Which risk factors for breast cancer are nonmodifiable (factors you cannot change)? 

Some risk factors for breast cancer cannot be changed but may help identify people who could benefit from enhanced screening, genetic counseling or closer monitoring.

Nonmodifiable risk factors for breast cancer include:

• Older age – The risk of breast cancer generally increases with age, with most cases diagnosed after age 50.
• Female sex – Women are more likely than men to develop breast cancer because of differences in breast tissue and hormone exposure.
• Personal history of breast cancer or a benign breast condition – Individuals who have previously had breast cancer face an increased risk of developing a new breast cancer. Certain noncancerous breast conditions, such as atypical hyperplasia and lobular carcinoma in situ (LCIS), are also associated with an elevated risk.
• Family history of breast or ovarian cancer – Having a close relative with breast or ovarian cancer may indicate an inherited predisposition to breast cancer.
• Inherited genetic mutations – Abnormal changes in certain genes, including BRCA1, BRCA2 and PALB2, can significantly increase breast cancer risk.
• Dense breast tissue – Women with dense breasts may have a higher risk of developing breast cancer, which often arises in glandular tissue. Dense tissue can also make abnormalities more difficult to detect on mammograms.
• Early menstruation or late menopause – Beginning menstruation before age 12 or reaching menopause after age 55 increases lifetime exposure to estrogen, which is linked to a higher risk of breast cancer.
• Previous radiation therapy – Individuals who received radiation therapy delivered to the chest at a young age may face an elevated risk of breast cancer later in life.

Can breast cancer be prevented?

There is no guaranteed way to prevent breast cancer. However, certain strategies may help reduce the risk. These include:

• Maintain a healthy body weight – Being overweight or obese, especially after menopause, may increase breast cancer risk. Achieving and sustaining a healthy weight may help lower that risk.
• Exercise regularly – Studies suggest that regular moderate to vigorous physical activity may help reduce breast cancer risk.
• Follow a healthy diet – Eating a balanced diet that includes fruits, vegetables, whole grains and lean proteins can support overall health and help maintain a healthy body weight, which may reduce breast cancer risk.
• Limit alcohol consumption – Reducing alcohol intake or abstaining may decrease the likelihood of developing breast cancer.
• Avoid tobacco use – Not smoking contributes to overall health and may help reduce cancer risk.
• Discuss hormone therapy risks with a health care provider – Women considering HRT should carefully review the potential benefits and risks with their physician.
• Receive recommended breast cancer screenings – Mammograms and other screening tools can help identify breast cancer before symptoms develop. When detected early, breast cancer is often more treatable.
• Consider genetic counseling if appropriate – Individuals with a strong personal or family history of breast cancer may benefit from genetic risk assessment and counseling.

Find the help you need for breast cancer at Moffitt Cancer Center

Understanding your individual risk for breast cancer can help you make informed decisions about screening, prevention and overall breast health. If you have a personal or family history of breast cancer, an inherited genetic mutation or other known risk factors, Moffitt's multispecialty team can provide a comprehensive risk assessment, advanced genetic counseling and testing and personalized recommendations based on your unique needs.

As a National Cancer Institute (NCI)-designated Comprehensive Cancer Center, Moffitt is committed to advancing the understanding of breast cancer through innovative research and patient-centered care. Our experts work closely with patients to evaluate breast cancer risk, support early detection efforts and develop individualized strategies for ongoing monitoring and risk management.

If you would like to learn more about breast cancer causes and risk factors, you are encouraged to talk with a specialist in Moffitt’s Don & Erika Wallace Comprehensive Breast Program. To request an appointment, call 1-888-663-3488 or submit a new patient registration form online. We do not require referrals.