Breast cancer

Breast cancer is a type of cancer that starts in the breast tissue. It can cause signs like finding a lump in the breast, noticing changes in the breast’s shape, seeing dimpling on the skin, milk rejection, fluid coming from the nipple, or a newly inverted nipple. When the disease spreads, it may cause bone pain, swollen lymph nodes, shortness of breath, or yellow skin.

Several things can increase the chance of developing breast cancer, such as obesity, not exercising enough, drinking alcohol, using hormone replacement therapy during menopause, being exposed to ionizing radiation, starting first menstruation early, having children later in life or not at all, and getting older. Some people are at higher risk because of family history or certain genes like BRCA mutations. Most breast cancers begin in the cells lining the milk ducts or in the lobules. To confirm if someone has breast cancer, doctors take a biopsy of the suspicious tissue.

Screening for breast cancer is important because finding it early, when it is small and has not spread, often leads to better outcomes. While there are different ways to screen, such as mammographic testing, it is still being studied to understand its benefits and possible risks. There are also ways to help prevent breast cancer in people at high risk, such as using certain medications like tamoxifen or raloxifene, or in some cases, surgical removal of both breasts. When breast cancer is found, treatments may include surgery, radiation therapy, chemotherapy, hormonal therapy, and targeted therapy.

Overall, many people with breast cancer can live long lives. In places like the United States and the UK, more than 90% of people live at least five more years after being diagnosed. Worldwide, breast cancer is the most common type of cancer in women, making up about a quarter of all cancer cases. It is far more common in women than in men.

Signs and symptoms

Most people with breast cancer do not feel any signs when it is first found; a test during a screening shows the growth. When signs are present, a new lump in the breast is the most common sign. Many breast lumps are not cancerous, but lumps that are painless, hard, and have uneven edges are more likely to be cancerous. Other signs include the skin of the breast feeling thicker or looking like orange peel, swelling or pain in the breast, dimpling, redness, or dryness of the breast skin, and pain or the nipple turning inward. Some people may notice unusual fluid coming from the breasts or swelling of the small parts under the arms or along the collar bone.

Some rarer types of breast cancer cause special signs. Up to 5% of people with breast cancer have a type where the growth blocks the small tubes in one breast, making the breast swell a lot and turn red over a few months. Up to 3% of people with breast cancer have a condition that causes red, scaly irritation on the nipple and the area around it.

When the growth grows larger, it can spread to other parts of the body, most often to the bones, liver, lungs, and brain. In the bones, this can cause swelling and pain, and weaken the bones. In the liver, it can cause pain in the belly, feeling sick, throwing up, and skin problems like rash or yellow skin. In the lungs, it can cause pain in the chest, trouble breathing, and coughing. In the brain, it can cause ongoing headaches, trouble speaking or seeing, memory problems, and changes in behavior.

Screening

Breast cancer screening means checking women who don’t have symptoms to find tumors early, when they are easier to treat. The most common test is called a mammogram, which uses a low-dose X-ray to take pictures of the breast. During this test, each breast is gently pressed between two plates. Tumors can show up as unusual shapes or small spots called microcalcifications in the images.

Mammograms can also show how dense the breast tissue is. Dense tissue can make it harder to see tumors. There are different ways to check for breast cancer, such as ultrasound, magnetic resonance imaging (MRI), or tomosynthesis, especially for women with very dense breasts.

Regular mammograms help lower the chances of dying from breast cancer. Many medical guidelines suggest women aged 50–70 get a mammogram every year. Some guidelines also recommend this for women aged 40–49. For women at higher risk, adding MRI to mammography can help find dangerous tumors earlier. Checking your own breasts for lumps does not lower the risk of dying from breast cancer. While clinical exams by a health professional are common, it is not known if they reduce the risk of dying from breast cancer. Screening is common in many wealthy countries but less so in poorer ones.

However, mammograms are not perfect. They can miss about 1 in 8 breast cancers and sometimes give false-positive results, which can cause worry and lead to extra tests like biopsies.

Diagnosis

If a lump or change in the breast is found during a mammogram or exam, more tests are done to learn more about it. Usually, this means another mammogram and an ultrasound. A small sample of tissue, called a biopsy, is then taken to check if the lump is cancer. Most lumps are not cancer but are changes in the breast tissue.

Breast cancers can be different types based on where they start and how they look under a microscope. The most common type starts in the tubes that carry milk. Other types are less common. Doctors also look at how fast the cancer cells are growing and whether they have certain proteins that can help decide how to treat it. This information is used to give each cancer a stage, which helps doctors plan the best care.

Management

The way doctors treat breast cancer depends on the person's health, the type of cancer, and how far it has spread.

Those whose cancer has not spread beyond the breast often have surgery to remove the tumor and some surrounding tissue. The surgery is chosen to keep as much healthy breast as possible, either by removing just the tumor (lumpectomy) or a larger part of the breast (partial mastectomy). For some people, the whole breast may need to be removed (full mastectomy). To help prevent the cancer from spreading, doctors may also remove nearby lymph nodes using a procedure called sentinel lymph node biopsy.

After surgery, many people receive radiotherapy to lower the chance of the cancer coming back. Radiation may be aimed at the whole breast or just the scar and chest wall, depending on the treatment. Radiation is usually given several times a week for several weeks. Some people also have a procedure called brachytherapy, where a small device with radioactive material is placed near the tumor site.

Chemotherapy can also help lower the chance of cancer returning. It is usually given in cycles over several months. Different drugs are used depending on the person's health and the type of cancer.

For people whose cancer makes too much of a certain protein (HER2-positive), special drugs like trastuzumab can help treat the cancer.

After chemotherapy, some people benefit from endocrine therapy, which lowers the amount of certain hormones that some breast cancers need to grow. This treatment is usually given for several years.

Prognosis

Breast cancer outcomes can vary a lot depending on where you live and how far the disease has spread when it is found. In places like the United States, the UK, South Korea, Japan, and Australia, over 90% of women live at least five years after being diagnosed. In China, this number is 82%, and in India, it is 66%.

How far the cancer has spread when it is found is very important. In the United States, 92% of women live at least five years after diagnosis. Those whose cancer is only in the breast, which is about two-thirds of cases, have the best outcomes and nearly all survive five years or more. For those whose cancer has spread to other parts of the body, the chances are much lower.

Some types of breast cancer, like triple-negative and inflammatory breast cancer, are more aggressive and have lower survival rates. Age also plays a role, with breast cancer in very young or very old people often having different outcomes.

Risk factors

Main article: Risk factors of breast cancer

Many things can affect the chance that someone might develop breast cancer. One big factor is related to a woman's body and hormones. Women who start their periods very early or go through menopause later may have a higher chance of getting breast cancer. Having a baby at a younger age can lower the risk, but this protection gets smaller the older a woman is when she has her first child. Breastfeeding can also lower the risk a little bit for each year a baby is breastfed. Certain treatments for menopause symptoms can raise the risk, depending on what kind is used and for how long.

Other factors include lifestyle choices. Drinking alcohol, even in small amounts, can increase the risk. Being overweight or having diabetes can also raise the chance of developing breast cancer. Smoking and not getting enough exercise are also linked to a higher risk. Some genes can play a role too. About one in ten cases of breast cancer run in families. Women with certain gene changes, like in the BRCA genes, have a much higher chance of getting breast cancer. Other health conditions and past radiation exposure to the chest can also affect risk.

Pathophysiology

See also: Carcinogenesis

Breast cancer happens when cells in the breast grow in an uncontrolled way. There are three main types of breast cancer. The most common type is called hormone receptor-positive. Another type is called triple-negative, and the third is ERBB2-positive. Hormone levels, especially estrogen, can affect the growth of breast cells. When estrogen is not balanced with progesterone, it can cause cells to grow too fast. This growth, along with damage to the cells' repair systems, can turn normal cells into cancer cells.

Like other cancers, breast cancer occurs when normal cells lose their ability to stop growing, stay in place, and die at the right time. Some important pathways that normally help cells self-destruct can become stuck "on" due to changes in the genes, which helps cancer cells survive. Certain genes, when changed, can also make cancer more likely, especially if a person inherits these changes.

Prevention

Women can help lower their chances of getting breast cancer by staying at a healthy weight, cutting down on alcohol, getting more exercise, and nursing their babies. These steps might lower the chances of breast cancer in many places around the world. Even simple activities like brisk walking can help at any age.

Doctors suggest eating lots of vegetables, fruits, whole grains, and beans. Foods with soluble fiber, citrus fruits, omega-3 fats found in fish, and soy products may also help lower the risk. In some cases, surgery to remove the breasts before cancer develops can greatly reduce risk, especially for women with certain genetic conditions. Certain medicines can also help lower risk for some women, but they come with other health considerations.

Epidemiology

Main article: Epidemiology of breast cancer

Breast cancer is the most common type of cancer in women in many countries, making up about 30% of all cancers in women. In 2022, around 2.3 million women were found to have breast cancer, and about 670,000 people passed away from it. The number of new cases is growing by about 3% each year because more people are living longer.

The chances of getting breast cancer differ around the world, often linking to how wealthy a country is. In wealthier countries, about 1 in 12 women may develop breast cancer during their lives. In countries with fewer resources, it’s about 1 in 27. This difference is mostly because women in wealthier countries often start having their periods earlier and have children later, which can raise the risk. Also, in lower-income countries, there is less access to checking for breast cancer early and treatments, so more people may pass away from the disease. In wealthy countries, about 1 in 71 women may pass away from breast cancer, while in lower-income countries, it’s about 1 in 48.

Breast cancer mostly affects women, with fewer than 1% of cases happening in men. Women can develop it as young as their teenage years, but the chance grows with age. Most cases—about 75%—happen in women older than 50 years old. Over a woman’s lifetime, the chance of developing breast cancer is about 1.5% by age 40, 3% by age 50, and more than 4% by age 70.

History

Breast cancer has been known for thousands of years. The oldest known case was found in Egypt, dating back over 4,200 years. Ancient doctors described changes in the breast, such as lumps or sores, and tried many treatments, but often felt there was no cure.

Over time, ideas about what caused breast cancer changed. Some thought it was due to imbalances inside the body. In the past, doctors sometimes removed the entire breast to try to stop the disease. One famous surgery, developed in the late 1800s, involved removing much tissue and muscles, which helped some patients live longer but was very hard on the body.

In more recent times, doctors have learned better ways to treat breast cancer. They now use different surgeries that save more of the breast and combine them with other treatments. Understanding how breast cancer grows and spreads has led to better care and more hope for those affected.

Society and culture

See also: Breast cancer awareness, List of people with breast cancer, and Cultural differences in breast cancer diagnosis and treatment

In the past, people did not talk much about breast cancer, often feeling ashamed. With better medical treatments, more people started talking about it and looking for help. In the 1930s and 1940s, groups began forming to support women with breast cancer. Later, in the 1980s and 1990s, more people spoke out about the disease as part of larger movements for women’s rights.

Pink ribbon

Main article: Pink ribbon

The pink ribbon is a well-known symbol for breast cancer awareness. People wear pink ribbons to show support for those affected by breast cancer or to show they like products linked to breast cancer causes. Many companies started using pink ribbons in the 1990s to raise money for breast cancer. However, some people feel that just wearing a pink ribbon does not really help solve the problem, and that it might even distract from real solutions. There are also concerns that it can reinforce unfair ideas about women.

Health disparities in breast cancer

Breast cancer is the most common cancer among women in the United States, affecting women of all backgrounds. However, there are differences in how often it occurs and how it is treated among various groups.

Some groups, like Black women, are more likely to be diagnosed with breast cancer at a younger age and may have a harder time getting treatment. This can be due to many reasons, including differences in healthcare access, money, and where they live. For example, Black women are often diagnosed at age 59, while white women are usually diagnosed at age 62. Getting regular check-ups and screenings is very important to find breast cancer early, when it is easier to treat. Unfortunately, some women, especially those with lower incomes or from certain backgrounds, are less likely to get these screenings, which can lead to later diagnoses.

Efforts to improve access to care, like offering help with language barriers, providing transportation, and using mobile clinics, can make a big difference. Including people from all backgrounds in research also helps doctors understand how breast cancer affects different groups and develop better treatments for everyone.

Special populations

Breast cancer is rare in men but can happen. It usually shows up as a lump in the breast. Men with certain health conditions or genetic changes may have a higher chance of getting it. Treatment often includes surgery and sometimes radiation.

Diagnosing breast cancer during pregnancy can be tricky because normal pregnancy changes can hide the signs. Doctors use the same tests as for others, but they avoid certain X-rays. Some treatments are put off until after the baby is born, and breastfeeding may not be possible if certain medicines are used. The outlook for pregnant women with breast cancer is usually similar to others of the same age.

Research

Scientists are always looking for new ways to treat breast cancer. They test new medicines, combinations of medicines, and different surgery and radiation methods. They study things like special treatments that target cancer cells, vaccines, therapies using viruses, gene changes, and immune system treatments.

Each year, important meetings happen where researchers share their newest findings. These meetings help doctors decide the best ways to treat different people with breast cancer.

Some studies look at ways to lower the chance of getting breast cancer. For example, a medicine called fenretinide is being tested to see if it can help prevent breast cancer. Doctors also study the best ways to use antibiotics before surgery to keep people from getting infections.

Cryoablation, a method that uses very cold temperatures, is being tested as a possible alternative to surgery for small breast cancers. It might be an option for people who cannot have surgery.

Much of what we know about breast cancer comes from studying cells taken from cancer tumors. These cells help scientists understand how breast cancer grows and how to stop it. The first breast cancer cell line was created in 1958, and since then, scientists have created about 100 different cell lines to study. Many of these cell lines come from cancers that have spread beyond the breast.

Other animals

Breast cancer can also happen in animals besides humans. For example, there are conditions called mammary tumors in other mammals. Scientists also use special mice to study how breast cancer spreads in the body.

Mammary tumor for breast cancer in other animals
Mouse models of breast cancer metastasis