Breast Cancer: Causes, Symptoms, Risk Factors & Prevention

Introduction

Breast cancer is a disease in which abnormal cells in the breast grow out of control and can form a tumor. It can occur in women and, less commonly, in men. According to the World Health Organization (WHO), approximately 2.4 million women were diagnosed with breast cancer worldwide in 2024, and the disease caused an estimated 694,000 deaths.

Breast cancer can develop in different forms and may have different biological characteristics, which can influence how it is diagnosed and treated. Risk varies from person to person and can be influenced by factors such as age, family history, inherited genetic changes, previous breast conditions, alcohol use, physical activity, and other factors. Having a risk factor does not mean that someone will definitely develop breast cancer, and some people develop the disease without a known major risk factor.

Recognizing unusual breast changes and seeking appropriate medical evaluation can help with early diagnosis. Screening mammography is also used to detect breast cancer before symptoms appear in certain groups of people. Screening recommendations can vary according to age, personal risk, family history, and the guidance followed in a particular country.

This guide explains what breast cancer is, the main types, recognized risk factors, possible signs and symptoms, how doctors investigate suspicious changes, approaches to risk reduction, and why appropriate screening and medical evaluation matter. It is intended for general education and is not a substitute for individualized medical advice.

What This Guide Can and Cannot Tell You

This guide is designed to help readers understand general information about breast cancer, including common risk factors, possible symptoms, screening, and the types of tests healthcare professionals may use.

It cannot determine whether a particular breast lump, symptom, or imaging result is cancer. It also cannot determine which screening schedule, diagnostic test, or treatment is appropriate for an individual person.

Those decisions depend on personal circumstances and should be discussed with a qualified healthcare professional. The purpose of this article is to help readers understand the terminology and information they may encounter so they can have more informed conversations about their health.

What Is Breast Cancer?

Breast cancer develops when abnormal cells in the breast grow and divide in an uncontrolled way. These cells can form a tumor and, in some cases, invade nearby tissues or spread to other parts of the body.

Breast cancer can begin in different parts of the breast. Many breast cancers start in the cells lining the milk ducts, while others begin in the lobules, which are the glands that produce breast milk. Less common types can develop in other breast tissues.

If cancer cells spread beyond the breast to nearby lymph nodes or other parts of the body, the disease is known as metastatic breast cancer. Cancer can spread through the lymphatic system or bloodstream.

Not every breast lump or breast change is caused by cancer. Many breast conditions are benign, meaning they are not cancerous. However, a new or unusual breast change should be evaluated by a healthcare professional so that its cause can be determined.

Types of Breast Cancer

Breast cancer can be classified in several ways, including where it begins, whether it has invaded surrounding tissue, and certain biological features that can affect treatment. Some common types and subtypes include:

• Ductal carcinoma in situ (DCIS): DCIS is not invasive breast cancer because the abnormal cells have not spread beyond the milk duct, but some cases can develop into invasive breast cancer if untreated.
• Invasive ductal carcinoma (IDC): IDC begins in the cells lining a milk duct and then grows beyond the duct into nearby breast tissue. It is the most common type of invasive breast cancer.
• Invasive lobular carcinoma (ILC): ILC begins in the lobules, the glands that produce breast milk, and can spread into nearby breast tissue.
• Inflammatory breast cancer: This is a rare and more aggressive form of breast cancer that can cause redness, swelling, warmth, or a peau d’orange appearance of the breast. It may not produce a distinct lump.
• Triple-negative breast cancer: This type of breast cancer does not have receptors for estrogen or progesterone and does not have excess HER2 protein. Because it lacks these three common treatment targets, treatment options can differ from those used for some other breast cancers.

Doctors use imaging, biopsy, and laboratory testing to determine the type and characteristics of breast cancer. These findings help healthcare professionals determine the most appropriate treatment approach.

Breast Cancer Risk Factors

Breast cancer does not usually have one identifiable cause. It develops when genetic changes cause breast cells to grow and divide abnormally. Researchers have identified many factors that can increase the likelihood of developing breast cancer, but having a risk factor does not mean that a person will definitely develop the disease. Some people develop breast cancer without having any known risk factors other than age and sex.

Genetic and Biological Risk Factors

• Age: The risk of breast cancer generally increases with age. Most breast cancers are diagnosed in older adults, although breast cancer can occur at any age.
• Family history: Having a close relative, such as a mother, sister, or daughter, with breast cancer can increase risk. A family history of ovarian cancer may also be relevant because some inherited genetic mutations can increase the risk of both cancers.
• Inherited gene mutations: Inherited changes in genes such as BRCA1 and BRCA2 can substantially increase the risk of breast and ovarian cancers. People with a strong family history or other features suggesting inherited risk may benefit from discussing genetic counseling with a healthcare professional.
• Personal history of breast cancer: People who have previously had breast cancer may have an increased risk of developing another breast cancer.
• Dense breasts: Having dense breast tissue can increase breast cancer risk and can also make some abnormalities more difficult to detect on a mammogram.

Average-risk situation	Higher-risk situation
No known major inherited mutation	Known high-risk inherited mutation
No previous breast cancer	Previous breast cancer
No history of high-dose chest radiation at a young age	Previous high-dose chest radiation
Routine screening may be appropriate	Earlier or additional screening may be considered
Follow applicable local screening guidance	Discuss individualized risk management

These categories are simplified for educational purposes. A person’s actual risk depends on their complete medical and family history, so screening decisions should be individualized.

Lifestyle and Environmental Risk Factors

• Alcohol use: Drinking alcohol is associated with an increased risk of breast cancer. In general, the risk increases as alcohol consumption increases.
• Body weight after menopause: Having overweight or obesity after menopause is associated with a higher risk of breast cancer, partly because fat tissue can affect hormone levels.
• Physical inactivity: Regular physical activity is associated with a lower risk of breast cancer. Being physically active also supports healthy body weight and overall health.
• Previous radiation exposure: Radiation treatment involving the chest, particularly at a young age, can increase the risk of developing breast cancer later in life.
• Smoking: Smoking is linked to many cancers and other serious health conditions. Some research also suggests a relationship between cigarette smoking and breast cancer risk, although this association is less established than some other breast cancer risk factors.

Reproductive and Hormonal Factors

Some reproductive and hormonal factors can affect breast cancer risk because they influence lifetime exposure to certain hormones.

• Early menstruation: Beginning menstrual periods at a younger age can be associated with a slightly higher breast cancer risk.
• Later menopause: Reaching menopause at an older age can also be associated with increased risk.
• Age at first full-term pregnancy: Having a first full-term pregnancy at an older age is associated with a higher risk compared with having a first full-term pregnancy at a younger age.
• Breastfeeding: Breastfeeding may modestly lower breast cancer risk, although it does not eliminate the possibility of developing breast cancer.
• Menopausal hormone therapy: Some forms of hormone therapy used during or after menopause, particularly combined estrogen-progestin therapy, can increase breast cancer risk. The effect can depend on the type of therapy, duration of use, and individual circumstances.

Having one or more of these risk factors does not mean that breast cancer will develop. Likewise, many people diagnosed with breast cancer do not have a strong family history or another obvious risk factor. A healthcare professional can help assess individual risk and determine whether additional screening or genetic counseling may be appropriate.

Signs and Symptoms of Breast Cancer

Breast cancer does not cause the same symptoms in everyone, and some people may have no noticeable signs or symptoms. Possible warning signs include a new lump in the breast or underarm, thickening or swelling of part of the breast, changes in the skin such as dimpling or irritation, redness or flaky skin around the nipple, changes in the nipple, unusual nipple discharge including blood, changes in breast size or shape, or pain in the breast or nipple area.

These changes do not automatically mean that a person has breast cancer. Many breast changes and breast lumps are caused by conditions that are not cancer. However, a new, unusual, or persistent breast change should be evaluated by an appropriate healthcare professional rather than being diagnosed at home.

Possible signs and symptoms of breast cancer include:

• A new lump or thickened area: A new lump in the breast or underarm can be a possible sign of breast cancer. However, many breast lumps are caused by non-cancerous conditions.
• A change in breast size or shape: A noticeable change in the size, shape, or appearance of one breast or both breasts should be evaluated.
• Skin changes: The skin of the breast may become dimpled, puckered, red, swollen, or thicker than usual. In some cases, the skin can develop an appearance similar to the peel of an orange.
• Nipple changes: The nipple may become newly inverted or change in appearance. Scaling, crusting, or other unusual changes around the nipple should also be checked.
• Nipple discharge: Unusual discharge from the nipple, particularly discharge that is bloody or occurs without squeezing the nipple, should be evaluated by a healthcare professional.
• Changes in the breast or nipple area: Persistent changes in the appearance or texture of the breast or nipple can have several causes, but they should not be ignored.
• Breast pain: Breast pain is common and is usually caused by conditions other than cancer. However, persistent or unexplained breast pain, especially when accompanied by another breast change, should be discussed with a healthcare professional.

These symptoms do not necessarily mean that a person has breast cancer. Many breast changes have non-cancerous causes. However, a new, unusual, or persistent change should be evaluated rather than ignored.

What Should You Do If You Notice a Breast Change?

Not every breast change is caused by cancer. Breasts can naturally change over time, and many lumps or other changes have causes that are not cancer. However, a new or unusual change should not be diagnosed at home.

If you notice a new lump, nipple discharge that is not expected, a change in the appearance of the breast or nipple, skin changes, swelling, or another change that concerns you, arrange an evaluation with a qualified healthcare professional.

During an appointment, the healthcare professional may ask when you first noticed the change, whether it has changed over time, and whether you have experienced other symptoms. Depending on the findings and your individual circumstances, further examination or imaging may be recommended.

A useful approach is to record what you noticed and when it began. This information can help you describe the change accurately during your appointment.

Do not assume that a breast change is cancer, but do not ignore a persistent or concerning change simply because it does not hurt. Professional evaluation is the appropriate way to determine what may be causing it.

Diagnosis and Detection

If a person notices a new breast change or has an abnormal result on a screening test, a healthcare professional may recommend additional evaluation. The tests used depend on the person’s symptoms, age, breast characteristics, personal history, and other risk factors.

Clinical Breast Examination

A healthcare professional may examine the breasts and nearby areas for lumps, swelling, skin changes, nipple changes, or other abnormalities. A clinical examination can help determine whether further testing is needed.

Mammography

Mammography uses low-dose X-rays to create images of the breast. Screening mammography is performed in people who do not have signs or symptoms, while diagnostic mammography may be used to investigate a breast symptom or an abnormal finding from a screening test.

Breast Ultrasound

Breast ultrasound uses sound waves to produce images of breast tissue. It may be used to evaluate a breast lump or other abnormality and can help distinguish some fluid-filled cysts from solid masses. Ultrasound may also be used alongside mammography in certain situations.

Breast MRI

Breast magnetic resonance imaging (MRI) uses magnetic fields and radio waves to create detailed images of breast tissue. It may be recommended for some people who have a substantially higher risk of breast cancer or when additional imaging is needed to evaluate a particular finding.

Biopsy

A biopsy involves removing a sample of breast tissue or cells so that they can be examined under a microscope. A biopsy is generally needed to determine whether a suspicious breast abnormality is cancerous and, if cancer is present, to identify important characteristics of the cancer.

The healthcare professional will determine which tests are appropriate based on the individual’s symptoms, medical history, risk factors, and previous test results. An abnormal mammogram or other imaging result does not necessarily mean that a person has breast cancer.

Prevention and Risk Reduction

There is no guaranteed way to prevent breast cancer. Some risk factors, such as age, inherited gene mutations, and family history, cannot be changed. However, certain lifestyle choices and medical approaches may help reduce the risk of developing breast cancer.

Lifestyle-Based Risk Reduction

• Maintain a healthy weight: Maintaining a healthy weight, particularly after menopause, may help lower the risk of breast cancer. If you are trying to manage your weight, focus on sustainable eating habits and regular physical activity rather than rapid or extreme weight-loss methods.
• Stay physically active: Regular physical activity is associated with a lower risk of breast cancer. For general health, adults are generally advised to get at least 150 minutes of moderate-intensity aerobic activity each week, along with muscle-strengthening activities on at least two days a week.
• Limit alcohol: Alcohol consumption is associated with an increased risk of breast cancer. The less alcohol a person drinks, the lower their breast cancer risk is likely to be. People who do not drink alcohol do not need to start drinking for health reasons.
• Choose a balanced diet: A balanced eating pattern that includes vegetables, fruits, whole grains, legumes, and other nutrient-rich foods can support overall health and help with healthy weight management. No specific food or diet has been proven to prevent breast cancer on its own.
• Do not smoke: Avoiding tobacco is an important part of overall cancer prevention and general health. If you smoke, quitting can provide substantial health benefits.
• Breastfeed when possible: Breastfeeding may provide a modest reduction in breast cancer risk. However, breastfeeding is a personal decision and is not a guarantee against breast cancer.

Screening and Medical Risk Reduction

• Follow appropriate screening recommendations: Breast cancer screening recommendations vary by country, age, and individual risk. People at average risk should discuss the appropriate screening schedule with a healthcare professional, while people at higher risk may need earlier or additional screening.
• Discuss your personal risk: A healthcare professional can consider factors such as family history, previous breast conditions, inherited gene mutations, and other risk factors to help determine whether additional assessment is appropriate.
• Consider genetic counseling when appropriate: People with a strong family history of breast or ovarian cancer, certain patterns of cancer in their family, or known inherited mutations may benefit from genetic counseling. A genetic counselor can explain potential risks and testing options.
• Ask about risk-reducing treatments if you are at very high risk: Some people at substantially increased risk may be offered medications or, in selected situations, preventive surgery. These decisions involve potential benefits and risks and should be discussed with an appropriate healthcare professional.

Breast Cancer Screening and Early Detection

Screening recommendations depend on factors such as age, personal risk, family history, previous breast conditions, and the guidelines used in a particular country.

For example, the U.S. Preventive Services Task Force (USPSTF) currently recommends screening mammography every other year for women aged 40 to 74 who are at average risk of breast cancer. The recommendation is intended for people without signs or symptoms of breast cancer and does not apply to certain higher-risk groups, such as people with a known high-risk genetic mutation, a history of high-dose chest radiation at a young age, or previous breast cancer.

People at higher-than-average risk may need a different screening approach based on their individual circumstances. Anyone who notices a new breast change should not wait for their next routine screening appointment before seeking medical evaluation.

Because screening recommendations can differ between countries and may change as evidence develops, readers should check current guidance from their local health authority or discuss their individual screening needs with a qualified healthcare professional.

Breast Cancer Screening vs. Diagnostic Testing

Screening and diagnostic testing are related but serve different purposes.

Screening is performed when a person does not have a known breast problem or symptoms and is being checked according to an appropriate screening recommendation. Mammography is an example of a breast cancer screening test.

Diagnostic evaluation is different. It is used when a person has a breast symptom, an unusual finding, or an abnormal screening result that needs further investigation. Depending on the situation, diagnostic evaluation may involve additional imaging or a biopsy.

This distinction is important because an abnormal screening result does not automatically mean that a person has breast cancer. Additional evaluation may be needed to determine what caused the abnormal finding.

Likewise, a screening test is not a replacement for medical evaluation when someone develops a new or concerning breast change.

What Happens After an Abnormal Mammogram?

An abnormal mammogram does not automatically mean that breast cancer is present. A screening mammogram can identify an area that needs a closer look, and additional evaluation may be recommended before a diagnosis can be made.

Depending on the finding, a healthcare professional may recommend additional mammographic images, breast ultrasound, or another form of imaging. In some situations, a biopsy may be recommended to examine cells or tissue under a microscope.

The exact next step depends on what was seen on the imaging, the person’s symptoms and medical history, and other individual factors. It is therefore not possible to determine the cause of an abnormal mammogram from the screening result alone.

If you receive an abnormal screening result, follow up with the healthcare professional or facility that arranged the examination and ask what additional evaluation is recommended.

What Does Having a Risk Factor Actually Mean?

A breast cancer risk factor is something associated with a higher likelihood of developing the disease. It does not mean that a person will definitely develop breast cancer.

Likewise, not having a recognized risk factor does not guarantee that someone will never develop breast cancer. Breast cancer can occur in people who do not have an obvious major risk factor.

Risk is also not the same for everyone. Age, family history, inherited genetic changes, previous medical history, breast characteristics, lifestyle factors, and other circumstances can interact in different ways.

If you have a strong family history of breast or ovarian cancer, know that you carry a cancer-associated genetic variant, or have another reason to believe you may be at increased risk, discuss your individual situation with a qualified healthcare professional. They can determine whether additional risk assessment, genetic counseling, or a different screening approach may be appropriate.

Living With and Beyond Breast Cancer

A breast cancer diagnosis can affect a person’s physical health, emotional well-being, relationships, work, and daily life. The experience can also continue to affect someone after treatment has ended.

Support from family members, friends, support groups, counselors, and healthcare professionals can help people cope with the emotional and practical challenges of diagnosis and treatment. Some people may experience anxiety, sadness, fatigue, changes in body image, or concerns about the cancer returning.

After treatment, follow-up care can help monitor health and address ongoing or new concerns. Survivorship care may include follow-up appointments, management of treatment-related side effects, emotional support, healthy lifestyle habits, and guidance about returning to normal activities.

Everyone’s experience with breast cancer is different. People who are struggling emotionally or having difficulty managing symptoms after treatment should discuss their concerns with their healthcare team so they can receive appropriate support.

Common Breast Cancer Misunderstandings

A breast lump always means cancer

Not necessarily. Many breast lumps are caused by non-cancerous conditions. However, a new or unusual lump should be evaluated by a healthcare professional rather than diagnosed at home.

An abnormal mammogram means I have cancer

Not necessarily. An abnormal screening result may simply mean that additional imaging or evaluation is needed. A screening result alone does not establish a cancer diagnosis.

If breast cancer doesn’t hurt, it isn’t serious

This is not reliable. Breast cancer does not always cause pain, particularly when it is first detected. New or unusual breast changes should be evaluated regardless of whether they are painful.

I don’t have a family history, so I cannot develop breast cancer

Incorrect. Family history can increase risk, but breast cancer can also occur in people without a known family history.

Men cannot develop breast cancer

Incorrect. Breast cancer can occur in men, although it is much less common than in women.

Having a risk factor means I will develop breast cancer

No. A risk factor increases the likelihood of developing a disease but does not mean that the disease will definitely occur.

Questions to Ask Your Healthcare Professional

If you are being evaluated for a breast change, an abnormal screening result, or a higher-than-average risk of breast cancer, you may find it helpful to ask:

• What did the examination or imaging show?
• Do I need additional testing?
• What is the purpose of the recommended test?
• If a biopsy is recommended, why is it needed?
• When should I expect the results?
• Does my family history affect my breast cancer risk?
• Should I discuss genetic counseling or testing?
• What screening schedule is appropriate for my individual risk?
• Are there lifestyle or other risk-reduction measures that may be appropriate for me?
• Who should I contact if I notice another breast change?

Write down important questions before an appointment and bring relevant medical or family-history information if available. Your healthcare professional can explain which tests, screening schedules, or other steps are appropriate for your individual circumstances.

Conclusion

Breast cancer can develop for many reasons, and risk is influenced by factors such as age, family history, inherited gene mutations, reproductive history, alcohol use, body weight, physical activity, and previous radiation exposure. Having a risk factor does not mean that breast cancer will develop, and some people develop the disease without an obvious risk factor.

Knowing the possible signs and symptoms, following appropriate screening recommendations, and discussing personal risk factors with a healthcare professional can support early detection and informed decisions about breast health. Maintaining a healthy weight, staying physically active, limiting alcohol, avoiding tobacco, and following a balanced diet may also help reduce risk.

If you notice a new or unusual breast change, do not wait for a routine screening appointment to have it evaluated. A healthcare professional can help determine the cause and recommend appropriate testing when needed.

Disclaimer

This article is intended for general educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. If you have a new breast lump, breast change, concerning symptom, or questions about your breast cancer risk or screening, speak with a qualified healthcare professional. Do not delay or avoid medical care because of information presented in this article.

Key Takeaways

• Breast cancer is a group of diseases involving abnormal growth of cells in breast tissue.
• Breast cancer can occur in both women and men, although it is much more common in women.
• Risk factors can increase the likelihood of developing breast cancer but do not mean that someone will definitely develop it.
• A new breast lump or other unusual breast change should be evaluated by an appropriate healthcare professional.
• Screening and diagnostic testing are not the same thing.
• An abnormal screening result does not automatically mean that cancer is present.
• Screening recommendations depend on factors such as age and individual risk and can vary between countries.
• Reliable medical information should be used alongside advice from qualified healthcare professionals when making personal health decisions.

Frequently Asked Questions

How old should I be when I start getting mammograms?

Screening recommendations vary by country, organization, and individual risk. In the United States, the U.S. Preventive Services Task Force recommends screening mammograms every two years for women ages 40 to 74 who are at average risk. People with a higher risk of breast cancer may need to begin screening earlier or have additional screening. Discuss your personal risk and screening schedule with a healthcare professional.

Can men get breast cancer?

Yes. Although breast cancer is much less common in men than in women, men can develop breast cancer. A new lump, nipple change, skin change, or unusual nipple discharge should be evaluated by a healthcare professional.

Does every breast lump mean cancer?

No. Many breast lumps are caused by non-cancerous conditions, such as cysts or fibroadenomas. However, a new, persistent, or unusual lump should be evaluated by a healthcare professional to determine its cause.

How often should I perform a breast self-exam?

Routine breast self-examination is not a substitute for recommended breast cancer screening. Instead, people can practice breast self-awareness by becoming familiar with the normal appearance and feel of their breasts and reporting new or unusual changes to a healthcare professional. If you notice a concerning change, seek medical advice rather than waiting for your next screening appointment.

Does having a BRCA1 or BRCA2 mutation mean I will develop breast cancer?

No. Certain inherited BRCA1 or BRCA2 mutations can substantially increase the lifetime risk of breast cancer, but they do not mean that cancer will definitely develop. People who have a known mutation or a strong family history may benefit from genetic counseling and a personalized risk-management plan.

Can underwire bras or antiperspirants cause breast cancer?

There is no good scientific evidence that wearing an underwire bra or using antiperspirants or deodorants causes breast cancer. These products have been studied because of common concerns about their possible effects, but major cancer organizations have not found convincing evidence that they increase breast cancer risk.

Sources and Medical Information

This article was researched using information from established public-health and cancer organizations, including the World Health Organization (WHO), Centers for Disease Control and Prevention (CDC), National Cancer Institute (NCI), and U.S. Preventive Services Task Force (USPSTF). Medical recommendations and statistics can change as evidence develops, so readers should consult current guidance and a qualified healthcare professional for personal medical decisions.

The sources below are provided so readers can review the evidence and guidance used to prepare this article.

References

• World Health Organization (WHO). Breast Cancer
• Centers for Disease Control and Prevention (CDC). Breast Cancer Risk Factors.
• Centers for Disease Control and Prevention (CDC). Symptoms of Breast Cancer.
• National Cancer Institute (NCI). Breast Cancer Causes and Risk Factors.
• National Cancer Institute (NCI). Mammograms.

 

Written by: Zaheer Abbas
Health & Wellness Writer

Last updated: January 21, 2026

This article was researched using information from established health organizations and medical authorities, including the World Health Organization (WHO), Centers for Disease Control and Prevention (CDC), and National Cancer Institute (NCI). It is intended to provide general educational information and does not replace individualized medical advice.