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Breast Cancer

Written by Ada’s Medical Knowledge Team

Updated on

What is breast cancer?

Breast cancer is the most common cancer in women. It is estimated that about one in eight women in the U.S. will develop breast cancer. 1 Breast cancer is most common in women over 50 years of age, though it can occur in younger women and, rarely, in men.

Although there may be no symptoms in the early stages, some people may have a painless lump in the breast, skin changes on the breast or discharge from the nipple.

Testing people with no symptoms, known as screening, is important to diagnose breast cancer in the early stages. Breast cancer that is discovered early has a good chance of recovery and cure.

If diagnosed early, surgery to remove the tissue affected by breast cancer in its entirety, along with local radiation therapy, may cure a person of this condition. If diagnosed at a later stage, when the breast cancer has spread, treatments that affect the whole body, such as chemotherapy, are often necessary.

Always seek medical attention if breast cancer is suspected. However, there are less serious causes for changes in the breast that are more common, such as fibrocystic breasts.

Types of breast cancer

There are many types of breast cancer. Sometimes, one breast tumor can be a combination of two or several different types. Breast cancer types include the following: 2 3

In-situ breast cancer

The female breast is made up of sections called lobes. Each of these is made up of many smaller lobules, which produce milk in nursing women. Lobes and lobules are connected by milk ducts, which act as tubes to carry the milk to the nipple. These breast structures are generally where breast cancer begins to form. In its earliest stage, it is known as in-situ breast cancer.

Ductal carcinoma in situ (DCIS)

DCIS is considered by some doctors to be an early form of breast cancer and by others to be a precancerous condition, which may develop into cancer. In DCIS, there are cancerous cells inside the walls of the breast’s milk ducts, but they have not grown through the walls of the ducts.

DCIS is highly curable through surgery to remove the affected area and prevent the possibility of these cells spreading to surrounding breast tissue. Sometimes, radiation therapy is necessary after surgery. Chemotherapy is not necessary for women with DCIS.

Lobular carcinoma in situ (LCIS)

LCIS is not actually considered to be cancerous. In LCIS, cells that are like cancer cells are growing in the lobules of the breast, but they have not grown through the walls of the lobules.

LCIS does not require treatment, but women with LCIS may be recommended for more regular screenings, as they are considered to be at higher risk of developing breast cancer.

Invasive breast cancer

Invasive breast cancer of no special type (NST), previously known as invasive ductal breast cancer, not otherwise specified (NOS), is the most common type of breast cancer, making up about 8 out of 10 invasive breast cancers, i.e. cancers that have spread beyond the initial layer of tissue where they developed and are growing into surrounding, healthy tissues.

Invasive lobular cancer is another type of invasive breast cancer, which starts in the milk-producing glands.

Inflammatory breast cancer

This type of breast cancer is caused by cancer cells blocking lymph vessels in the skin. The lymph vessels are part of the immune system. They normally drain excess tissue fluid away from the body tissues and organs. The lymph vessels can’t do this job properly if they are blocked. Instead, they cause symptoms of inflammation, such as swelling and redness. Inflammatory breast cancer is uncommon, accounting for 1 to 5 percent of all breast cancers.

Triple negative breast cancer

Breast cancer cells often have receptors that hormones or other proteins can attach to and stimulate the cancer to grow. Receptor cells can be used to treat many breast cancers by blocking the hormones or proteins from attaching to the receptors. Triple negative breast cancer does not have the following key receptors: 4

  • Estrogen
  • Progesterone
  • HER2 protein

This means that hormone treatment and the targeted cancer drug trastuzumab do not work on triple negative cancers. Instead, the main treatments for triple negative breast cancer are surgery, radiation therapy and chemotherapy.

Triple negative breast cancer is usually diagnosed using a sample of the cancer to test the cells for these receptors, after a biopsy or after surgery to remove the cancer.

Good to know: Triple negative cancer is an uncommon type of breast cancer; about 15 out of every 100 breast cancers are triple negative. Basal-like breast cancer, a rare type of breast cancer in which the cells resemble the basal cells that line the breast ducts, is normally triple negative.

HER2 breast cancer

HER2-positive breast cancer has receptors for HER2 proteins.

These cancers tend to grow faster and may have a worse prognosis. They are often successfully treated, however, with targeted therapies aimed at the HER2 protein, such as trastuzumab.

Paget disease of the nipple

Also known as Paget disease of the breast, Paget’s disease of the nipple is a rare type of breast cancer.

It starts in the breast ducts before spreading to the skin of the nipple and then the areola – the dark line circling the nipple. It usually affects only one nipple and can look very similar to eczema, with crusted, scaly and red skin, sometimes itching or burning. Blood or yellow fluid may be coming out of the nipple. The nipple may also look flat or inverted.

Paget disease usually develops from ductal carcinoma in situ (DCIS) or infiltrating ductal carcinoma. 5

Breast cancer symptoms

Early signs of breast cancer include a painless lump or mass in the breast. However, many people with early breast cancer will have no symptoms at all.

The most common symptoms of breast cancer include: 6 7

  • A painless lump or mass in the breast: This may not be seen, but might be felt.
  • Change in breast size or shape: For example, one breast might become larger or lower than the other.
  • Changes in skin texture: This could be thickening, puckering or dimpling of the skin of the breast.
  • Change in breast color: The breast might look red or inflamed.
  • Change in nipple shape: The nipple of the affected breast might become inverted when it normally points out.
  • Rash or crusting over the nipple: This also may affect the surrounding area.
  • Nipple discharge: Discharge from one nipple, especially if it’s bloodstained
  • Pain in a breast or armpit that is there all or almost all of the time
  • Lumps or swellings in the armpit or around the collarbone

Good to know: Most breast lumps are not cancerous; 80 percent of those tested with a biopsy are not found to be cancerous. 8 However, it is important to see a doctor as soon as possible if a person suspects they may have breast cancer. For a free symptom assessment, try the Ada app.


Breast cancer occurs when abnormal cells develop in the breast tissue and grow quickly and uncontrollably. These cells destroy and replace the normal breast tissue and may spread through the body.

Risk factors

Risk factors for breast cancer include: 9 10

  • Gender: Being female
  • Age: Being older than 50
  • Family history: Having a close relative who has either breast, uterine or ovarian cancer
  • Genetic inheritance: particularly the BRCA-1 and BRCA-2 genes
  • A previous diagnosis of breast cancer
  • Being overweight: Fat cells produce estrogen
  • Excessive alcohol consumption: Research shows that drinking alcoholic beverages increases the risk of hormone-receptor-positive breast cancer, as it can increase levels of estrogen and other hormones associated with hormone-receptor-positive breast cancer. Alcohol also may increase breast cancer risk by damaging DNA in cells
  • Using tobacco products: This is linked to a higher risk of breast cancer in younger, premenopausal women. There may also be a link in postmenopausal women between very heavy second-hand smoke exposure and breast cancer risk
  • Not being physically active: Exercise consumes and controls blood sugar and limits blood levels of insulin growth factor, a hormone that can affect how blood cells grow and behave
  • Not having children: Women who have not had a full-term pregnancy or have their first child after age 30 may have a higher risk of breast cancer compared with those women who have given birth before the age of 30
  • Not breastfeeding: Breastfeeding can lower the risk, especially if done for longer than one year
  • Hormone replacement therapy (HRT): Some types of HRT use after menopause, though not all, may result in an increased risk

Breast cancer and COVID-19"

COVID-19 can cause severe symptoms in patients being treated for breast cancer. This is because cancer therapy weakens the immune system, which puts you at a higher risk of contracting the coronavirus. Taking the necessary precautions and getting tested as soon as possible if you start experiencing symptoms is crucial. Treatment options are available.

Diagnosis of breast cancer

Diagnosis is usually made during breast cancer screening. Screening is important because it allows breast cancer to be detected and treated at an early stage. The earlier the cancer is found, the better the chances of surviving it. Breast cancer screening is normally done by mammogram, a type of X-Ray scan. 11

In order to rule out a cancer diagnosis, a test, known as a biopsy may be carried out that removes tissue or sometimes fluid from an area suspected to be cancerous. Local anesthetic may be administered, depending on the type of biopsy used.

If you are worried that you may be experiencing symptoms of breast cancer, try using the Ada app to find out more.


A mammogram is an X-ray of the breasts that looks for changes that may be signs of breast cancer, such as small white spots called calcifications and lumps or tumors.

A mammogram is the best breast cancer screening test, though it is possible to have a mammogram give an incorrect result, miss the presence of a cancer or show cancer-like structures which are in fact benign. 12

Women under the age of 40 do not often have a mammogram. This is because it is difficult to obtain a clear picture of younger women’s breasts, which are denser, using a mammogram.


Ultrasound may be used to look at breast changes that cannot be seen on a mammogram, such as if a woman has very dense breasts or as a follow-up test if a mammogram shows a breast lump.


A biopsy is a test that removes tissue or sometimes fluid from a part of the body. Cells are then examined under a microscope and further tested to check for the presence of breast cancer.

Good to know: About 80 percent of women who have breast biopsies do not have breast cancer.

There are three types of biopsy that may be used to test for breast cancer: 2 13

Fine needle aspiration

If the lump is easily accessible or is likely to be filled with fluid, a doctor may perform a fine needle aspiration (FNA), in which fluid is drawn through a needle. The lump should collapse once the fluid inside has been drawn. If the lump persists, the cells in the sample may be examined.

Core needle biopsy

This involves using a larger needle through which a small amount of tissue can be removed. Local anesthetic will be used.

Surgical biopsy

A surgical biopsy is done with local anesthesia and, usually, sedation. This involves removal of all or part of an abnormal lump.

Breast cancer stages

Once breast cancer is diagnosed, doctors will try to find out whether it has spread and, if so, how far, in a process known as staging.

The staging system most often used for breast cancer is the American Joint Committee on Cancer (AJCC) TNM system, based on tumor size, number and location of lymph nodes 14 with cancer.

The cancer may then be given a number stage from 1 to 4, often followed by subdivisions of a, b or c. The lower the number, the less the cancer has spread. A general overview of the stages is as follows: 15 16

Stage 0 breast cancer is the earliest stage, also known as carcinoma in situ. This stage is used to describe breast cancer that is within the breast ducts or milk glands and has not spread. It is usually curable by surgery to remove the affected area.

Stage 1 breast cancer is invasive, meaning it has invaded other surrounding tissues and may involve N1mic, which means that there is micrometastasis, i.e. tiny amounts of cancer cells, in nearby lymph nodes in tiny amounts.

Stage 2 breast cancer means the tumor has grown to somewhere between the size of a walnut and a lime, spread to nearby lymph nodes, or both.

**Stage 3 breast cancer has not spread to bones or organs, but is considered advanced and harder to treat. It may have spread to a significant number of lymph nodes or grown into the chest wall or skin around the breast.

Stage 4 breast cancer has spread to distant sites, most commonly the bones, lungs, liver and brain, in what is known as metastasis.

Other factors may also affect what stage is given to a case of breast cancer, including: 15 16

  • Tumor grade: How abnormal the cancer cells look under the microscope
  • Estrogen and progesterone receptor status: Whether the cancer cells have receptors for these hormones
  • HER2 status: Whether the cancer cells are overproducing the HER2 protein
  • Oncotype DX score: If the cancer is estrogen-receptor-positive, HER2-negative and there is no cancer in the lymph nodes

Treatment of breast cancer

The extent of the treatment required for breast cancer depends on the extent to which it has spread and the exact type of cancer. It may be possible to remove the entirety of the affected area(s) with surgery and localised radiotherapy. However, breast cancer that has spread to multiple sites within the body may require a combined approach.

Treatment options for breast cancer will depend on the overall health of the affected person, their specific medical circumstances and how far the cancer has spread.


There are many different types of surgery for breast cancer. What a doctor recommends will depend on the state of the cancer and the affected person’s wishes and feelings. Types of breast cancer surgery may include: 17

  • Breast conserving surgery, which removes only the area of the cancer
  • Mastectomy – surgery to remove the whole breast
  • Breast reconstruction
  • Removing the lymph nodes


Also known as radiotherapy, radiation therapy uses X-rays to destroy cancer cells. Side effects of radiation for breast cancer are normally relatively easy to tolerate and are mostly limited to the treated area in the form of rashes and other skin irritation. 18 A doctor will be able to advise on how best to manage the side effects, should they occur.


The general aims of chemotherapy treatment for breast cancer are to destroy any cancer cells and increase the likelihood of recovery.

Chemotherapy can sometimes have unpleasant side effects, such as hair loss, nausea and vomiting, fatigue and pain. A doctor will be able to advise on how best to manage the side effects, should they occur.

Read more about Chemotherapy Side Effects ».

Hormone therapy

Some breast cancers, known as receptor-positive cancers, are stimulated by estrogen or progesterone, hormones produced in the body that help the cancer to grow.

Hormone therapy, also known as endocrine therapy, is a treatment that blocks hormones in the body from acting on breast cancer cells or lowers the levels present. 19

Hormone therapy can sometimes have side effects, such as hot flushes, reduced libido and mood changes. A doctor will be able to advise on how best to manage the side effects.


Immunotherapy aims to activate a person’s immune system to recognize and kill their tumors.

Some are now approved for treatment of certain HER2 breast cancers, while others are being studied further. 20


The causes of breast cancer are not fully understood, so it’s not known if it can be prevented. However, there are some general preventive measures that may be taken and some treatments available to reduce the risk in women who have a higher risk of developing the condition.

General preventive measures

General measures that may help prevent breast cancer include: 21 22

Regular exercise and a healthy, balanced diet: Maintaining a healthy weight can help prevent many forms of cancer, including breast cancer.

Breastfeeding: This has been found to lower the risk of developing breast cancer. It may be because women don’t ovulate as regularly when they’re breastfeeding, so their estrogen levels remain more stable.

Preventative treatments

Women who are at high risk of breast cancer, as determined by factors such as age, family medical history and genetic testing, may be offered medical treatments to prevent breast cancer.

The two main treatments that may help prevent breast cancer are: 21 23


This can be used to treat breast cancer, to prevent recurrence and to reduce the chance of developing the condition for women at high risk.

This surgery can reduce risk of breast cancer by up to 90 percent. However, like all operations, there’s a risk of complications, and some women experience significant effects on their body image and sexual relationships.

Surgical breast reconstruction is also available. In some cases, a nipple-sparing mastectomy may be available.


Hormonal medications are available to reduce a person’s risk of developing breast cancer.

However, these medications may cause side effects such as hot flushes, nausea and tiredness and have a small risk of more serious problems, such as osteoporosis, blood clots or womb cancer.


Prognosis is estimated by looking at what happened over to many years to large groups of people diagnosed with the same stage of cancer, known as survival rates.

Survival rates show what percentage of people live for a certain length of time after being diagnosed with cancer.

Survival rates are generally sorted into 5-year and 10-year time brackets. Because the statistic is based on people diagnosed over five years ago, the outlook may be better for those diagnosed today, since there are continuing improvements in treatment.

Survival rates include people who are free of disease or who experience few symptoms, as well as those who are still being treated for cancer, those who will survive for many more years and those who will not live much longer than the time bracket given.

Five-year survival rates for people with breast cancer in the U.S. are currently as follows: 24

  • Localized breast cancer: About 62 percent of breast cancers are found when they are localized, meaning they have not spread beyond the breast. The five-year survival rate is about 99 percent.
  • Locally advanced breast cancer: If the cancer has spread to nearby lymph nodes, this is known as locally advanced cancer. The five-year survival rate is about 85 percent.
  • Metastatic cancer: If the cancer has spread further to other parts of the body, it is known as metastatic cancer. The five-year survival rate is about 27 percent.

The overall five-year survival rate for breast cancer is about 90 percent.

Good to know: Survival rates do not predict what will happen to someone. Treatment and responses to treatment vary greatly.


Q: Does abortion increase the risk of breast cancer?
A: No. There is no evidence for a causal relationship between breast cancer and abortion. Early studies of the relationship between prior-induced abortion and breast cancer risk claimed to show a link, but were methodologically flawed.

For instance, one such study relied upon people volunteering the information that they had once had an abortion. A key methodological consideration in interpreting the evidence for any relationship between abortion and breast cancer risk is the sensitive nature of abortion, which means, for example, people may be too embarrassed or unwilling to disclose that they had once had an abortion. This could affect the accuracy in retrospective studies that rely on this sensitive information being shared. 25

Another study did not take into account the role of socioeconomic status as a variable which could distort the true relationship between abortion and breast cancer: women from higher socioeconomic classes have more breast cancer incidences in general, likely due to factors such as higher hormonal contraceptive use and bearing fewer children and are also believed to have a greater preference for abortion when pregnant. 26 More rigorous recent studies demonstrate no causal relationship between induced abortion and a subsequent increase in breast cancer risk.

Q: Is breast cancer painful?
A: Breast pain is not commonly an early sign of breast cancer. However, there are some rare types of breast cancer that can commonly cause pain as one of the first symptoms. This includes inflammatory breast cancer, in which pain or tenderness is often one of the first symptoms, followed by reddening and dimpling of the skin, as well as Paget’s disease of the nipple, which can cause pain and burning as an early symptom. Most breast pain is due to normal changes in the breast resulting from changes in hormone levels. Some women have non-cancerous lumpy breast tissue called fibrocystic breasts, which may be more painful during certain times of the month. Certain medications can also cause breast pain. If a person experiences breast pain along with any other symptoms of breast cancer, as listed in the symptoms section above, they should contact their doctor.

Breast cancer is more likely to cause pain in more advanced stages, either if the tumor pushes into nearby healthy tissue or if the cancer spreads to other parts of the body, where it may cause pain. Pain can be a side effect of chemotherapy and radiation therapy treatment for breast cancer. For more information, see the resource on chemotherapy side effects.

Q: Is there a breast cancer cure?
A: There are many very good breast cancer treatments, which can often cure breast cancer. Treatment outcomes have also improved now that many are diagnosed at an early stage, due to mammogram screenings. Once breast cancer has spread, it becomes more difficult to cure. Certain types of breast cancer are more likely to be cured, such as infiltrative ductal carcinoma, the most common type of breast cancer, which is limited to the milk duct region and can almost always be cured if found before it has spread. Infiltrative lobular carcinoma is harder to cure as it often affects both breasts. 27 Hormone receptor-positive cancer has a better prognosis than triple negative cancer (see types of breast cancer).

Q: Is breast cancer hereditary?
A: Most breast cancers are not caused by inherited genetic factors. However, some people may inherit an increased risk of breast cancer. Inherited mutations in the BRCA1 and BRCA2 genes, which produce tumor suppressor proteins, can increase a person’s chance of developing breast cancer. These genes can be inherited from either the mother or the father. Not all people who inherit such mutated genes will develop cancer. 28

Q: What bras should I wear after breast cancer treatment?
A: After surgery and radiotherapy for breast cancer, it can take up to a year for the area to recover. During this time, a person can get bras to make them more comfortable and which may include any of the following features:

  • No underwiring: Underwires can be uncomfortable.
  • Fits on the loosest hook: There may be swelling after surgery. A bra that initially fits on the loosest hook can gradually be tightened as the swelling goes down.
  • High cotton content: Cotton is gentler on the skin and helps with staying cool if a person is experiencing hot flushes as a treatment side effect.
  • Bra strap cushions: These may make the straps more comfortable and secure.

Breast shape and size may change during and after treatment, so it’s a good idea to have one’s bra size measured before buying any new bras. Many lingerie shops have experienced bra fitters, who may have specialist training in helping women who have had, or are going to have, breast surgery.

Mastectomy bras for women who have had their breast(s) removed are available from specialist suppliers. Breast prosthesis may also be worn to replace all or part of a breast that has been removed. This is an artificial breast form that fits in a bra cup. If a person has not had an immediate reconstruction, in many cases, a temporary breast prosthesis will be provided after surgery. 29