Breast cancer is a disease where cells in the breast tissue grow abnormally and form tumors. It is one of the most frequently diagnosed cancers in women worldwide, though it can also affect men. While the diagnosis can feel overwhelming, advances in early detection and treatment have greatly improved survival rates and quality of life for many people living with this condition.
Epidemiology
Breast cancer represents a significant global health challenge. In 2022, approximately 2.3 million women worldwide received a breast cancer diagnosis, with an estimated 670,000 deaths attributed to the disease. The condition occurs in every country across the world, affecting women at any age after puberty, though rates increase significantly in later life.[4]
In the United States, breast cancer is the second most common cancer diagnosed in women, following non-melanoma skin cancer. An estimated 316,950 new cases were expected in 2025, with about 42,170 deaths among women. Despite these numbers, fewer than one in eight women diagnosed with breast cancer will die from the disease, largely due to improvements in screening and treatment.[1][9]
The disease primarily affects women aged 50 and older. Most breast cancers are diagnosed after this age, though younger women can also develop the condition. Approximately 99% of breast cancer cases occur in women, while men account for about 0.5 to 1% of all cases.[4][15]
Global disparities in breast cancer outcomes reveal striking inequalities. In countries with very high Human Development Index scores, one in 12 women will be diagnosed with breast cancer during their lifetime, and one in 71 will die from it. In contrast, in countries with low Human Development Index scores, only one in 27 women is diagnosed with breast cancer, but one in 48 will die from it. This suggests that while the disease is less common in lower-resource settings, survival rates are significantly worse.[4]
Causes
Breast cancer develops when cells in the breast tissue undergo mutations, meaning their genetic material becomes damaged or altered. These mutations cause cells to grow and divide in an uncontrolled way, eventually forming tumors. The exact reasons why these mutations occur are not fully understood, but they appear to result from a complex interaction between genetic, hormonal, and environmental factors.[1]
The disease can begin in different parts of the breast. The breast contains milk-producing glands called lobules, tubes called ducts that carry milk to the nipple, and connective tissue made of fibrous and fatty material that holds everything together. Most breast cancers start in the ducts or lobules. When cancer cells remain within these structures, they are called “in situ.” When they spread into nearby breast tissue, they become “invasive.”[2][6]
A small percentage of breast cancers, approximately 5% to 10%, are caused by inherited genetic mutations passed down through families. The most well-known of these are mutations in genes called BRCA1 and BRCA2. Women who inherit these genetic changes have a significantly higher lifetime risk of developing breast and ovarian cancer. Specific variants of these genes are more common in women of Jewish ancestry.[5]
Risk Factors
While any woman can develop breast cancer, certain factors increase the likelihood of the disease. The strongest risk factor is simply being female, as the vast majority of cases occur in women. Age is also critical—most breast cancers are diagnosed in women over 50, and risk continues to rise as women get older.[1][6]
Family history plays an important role. Women who have close blood relatives, such as a mother, sister, or daughter, with breast cancer face higher risk. This risk increases further if multiple family members have been affected or if the cancer occurred at a young age. However, it’s important to know that most women who develop breast cancer do not have a family history of the disease.[9]
Reproductive and hormonal factors influence breast cancer risk because estrogen and progesterone can stimulate the growth of some breast cancer cells. Women who started their menstrual periods before age 12 or entered menopause after age 55 have longer lifetime exposure to these hormones. Similarly, women who have never had children or who had their first child after age 30 face slightly elevated risk. On the other hand, breastfeeding appears to offer some protective effect.[6][9]
Lifestyle factors also matter. Drinking alcohol increases breast cancer risk, even in small amounts. Being overweight or obese after menopause raises risk because fatty tissue produces estrogen. Physical inactivity contributes to this problem as well. Women who take combination hormone replacement therapy, which includes both estrogen and progestin, face increased risk compared to those who do not use these medications.[6]
Having dense breasts, which means the breast tissue has more connective tissue than fatty tissue, makes it harder to detect cancer on mammograms and is also associated with higher risk. Previous radiation treatment to the chest area, especially during younger years, increases the likelihood of developing breast cancer later in life. Women who have already had breast cancer in one breast are at higher risk of developing a new cancer in the other breast or in a different part of the same breast.[6][9]
Symptoms
Breast cancer can affect the breasts in various ways, and symptoms can differ from person to person. In many cases, especially in countries with established screening programs, breast cancer is detected through routine mammograms before any symptoms appear. However, when symptoms do occur, they serve as important warning signs.[1][5]
The most commonly recognized symptom is a lump or thickening in the breast or underarm area. This lump may feel as small as a pea or larger, and it typically persists through a woman’s menstrual cycle rather than coming and going. Not all lumps are cancerous—many are caused by benign conditions like cysts or fibrocystic changes—but any new or unusual lump should be evaluated by a healthcare provider.[1][6]
Changes in the size, shape, or contour of the breast can indicate a problem. The breast may appear swollen or feel different than usual. Some women notice that one breast has become noticeably larger or has changed shape in a way that seems abnormal.[1]
Skin changes on the breast deserve attention. The skin may appear dimpled or puckered, resembling an orange peel. It might become red, purple, or darker than the surrounding skin. Some women develop scaly or inflamed skin on the breast or nipple area. These changes differ from normal variations and tend to persist over time.[1][6]
Nipple changes can signal breast cancer. The nipple may pull inward or become inverted when it previously pointed outward. Some people experience nipple discharge that is not breast milk, which may be clear, bloody, or another color. The nipple or surrounding area might feel painful or tender, though breast cancer often does not cause pain, especially in early stages.[1][6]
A particular type called inflammatory breast cancer presents differently. This rare, aggressive form causes the breast to appear red and feel warm. The skin may look dimpled like an orange peel, and the breast becomes swollen. These symptoms result from cancer cells blocking lymph vessels in the breast skin.[1][2]
It’s important to remember that many of these symptoms can also be caused by conditions that are not cancer. However, any persistent or concerning change should be evaluated by a healthcare professional. Early detection significantly improves treatment options and outcomes.[6]
Prevention
While there is no guaranteed way to prevent breast cancer entirely, certain steps can help reduce risk. Understanding which factors you can control empowers you to make informed decisions about your health.[6]
Maintaining a healthy body weight, especially after menopause, helps reduce risk. Excess body fat produces estrogen, which can promote the growth of some breast cancers. Combining a balanced diet rich in fruits, vegetables, and whole grains with regular physical activity supports weight management and overall health.[6]
Regular exercise offers protective benefits beyond weight control. Studies suggest that physical activity, whether it’s brisk walking, swimming, or other forms of movement, can lower breast cancer risk. Aim for at least 150 minutes of moderate-intensity activity each week, or 75 minutes of vigorous activity.[6]
Limiting alcohol consumption reduces risk. Even small amounts of alcohol have been linked to increased breast cancer rates. If you choose to drink, consider keeping intake as low as possible. Women who drink alcohol should be aware of this connection and make informed choices.[6]
For women considering hormone replacement therapy for menopause symptoms, it’s important to discuss the risks and benefits with a healthcare provider. Combination hormone therapy that includes both estrogen and progestin increases breast cancer risk. If hormone therapy is necessary, using it for the shortest time possible at the lowest effective dose may help minimize risk.[6]
Breastfeeding, when possible, appears to offer some protection against breast cancer. The longer a woman breastfeeds, the greater the protective effect may be. This is thought to occur because breastfeeding reduces lifetime exposure to estrogen by delaying the return of menstrual periods after childbirth.[6]
For women at very high risk due to genetic mutations or strong family history, risk-reducing medications may be an option. Drugs like tamoxifen or raloxifene can lower the chance of developing breast cancer in high-risk women. Some women with BRCA1 or BRCA2 mutations may consider preventive surgery to remove healthy breast tissue before cancer develops. These are significant decisions that require thorough discussion with healthcare providers and genetic counselors.[14]
Regular screening remains one of the most effective tools for reducing breast cancer deaths. While screening doesn’t prevent cancer, it allows for early detection when treatment is most effective. Mammograms can find cancers before they can be felt, often at a stage when they are more easily treated. Women should discuss with their healthcare providers when to start screening and how often to have mammograms based on their individual risk factors.[6]
Pathophysiology
Understanding what happens in the body when breast cancer develops helps clarify how the disease progresses and why various treatments work. Normal breast cells have built-in mechanisms that control when they grow, divide, and die. Breast cancer begins when these control mechanisms break down due to genetic mutations in the cell’s DNA.[1]
These mutations cause cells to ignore normal signals that tell them to stop growing. Instead, the abnormal cells continue dividing and accumulating. Unlike normal cells that have a programmed lifespan and die when they become old or damaged, cancer cells evade this death process and keep multiplying. Over time, these cells form a mass or tumor.[1]
The earliest form of breast cancer, called ductal carcinoma in situ or DCIS, remains confined within the milk ducts. At this stage, the cancer has not broken through the duct walls into surrounding breast tissue. DCIS is considered non-invasive and is not immediately life-threatening, but without treatment, it can progress to invasive cancer in up to 40% of cases.[2][14]
When cancer cells break through the duct or lobule walls and invade nearby breast tissue, the cancer becomes invasive. Invasive ductal carcinoma accounts for about 70% to 80% of all breast cancers. Invasive lobular carcinoma, which starts in the milk-producing lobules, represents about 10% to 15% of cases. These invasive cancers can continue spreading beyond the breast.[2][9]
Breast cancer cells can enter the lymphatic system, a network of vessels and nodes that filters fluid and helps fight infection. The lymph nodes closest to the breast are in the armpit area, called axillary nodes. Cancer cells that reach these nodes can then travel to other parts of the body through the lymphatic system or bloodstream. When breast cancer spreads to distant organs such as bones, lungs, liver, or brain, it is called metastatic breast cancer. These distant tumors are made up of breast cancer cells, not cells from the organ where they have spread.[9]
Many breast cancers are influenced by hormones, particularly estrogen and progesterone. Cancer cells may have receptors on their surface that allow these hormones to attach and stimulate cell growth. Cancers with estrogen receptors (ER-positive) or progesterone receptors (PR-positive) can be treated with hormone-blocking therapies. About 15% to 20% of breast cancers produce excess amounts of a protein called HER2, which promotes rapid cell growth. These HER2-positive cancers can be treated with drugs that target this protein.[1][15]
Triple-negative breast cancer lacks estrogen receptors, progesterone receptors, and does not overproduce HER2 protein. This type tends to grow and spread more quickly than other forms and has fewer targeted treatment options, making it more challenging to treat.[1]
As tumors grow, they can physically change the breast’s appearance and cause symptoms. Cancers that block lymph vessels in the breast skin cause inflammatory breast cancer, which makes the breast appear red, swollen, and warm. Cancer cells that reach the skin of the nipple cause Paget’s disease of the breast, which may look like a rash but is actually cancer.[1][2]
