Breast cancer

What is it?

The WHO defines breast cancer as “a disease in which abnormal cells in the breast grow out of control and form tumours”. The cancer cells start inside the milk ducts and/or the milk-producing lobules, and the earliest form (in situ) is not life-threatening and can be detected early. The cells may spread into the surrounding breast tissue (invasion), forming tumours that cause lumps or thickening, and invasive cancers may spread to nearby lymph nodes or other organs.

The CDC explains the three parts of the breast: the lobules, which are the glands that make milk; the ducts, which are tubes that carry milk to the nipple; and the connective tissue (fibrous and fatty tissue) that surrounds and holds everything in place. “Most breast cancers begin in the ducts or lobules”, and when it spreads to other parts of the body through the lymph nodes or blood it is called metastatic breast cancer.

Types according to the CDC: invasive ductal carcinoma (about 70% to 80% of cases) begins in the ducts and then spreads to other parts of the breast, and invasive lobular carcinoma (about 10% to 15%) begins in the lobules. Ductal carcinoma in situ (DCIS) has cells in the lining of the ducts only that have not spread, and it is a disease that may sometimes lead to invasive cancer. Other types include inflammatory breast cancer, Paget disease of the breast and triple-negative cancer (about 15%). MedlinePlus describes the ductal type as the most common, and the inflammatory type and Paget disease as rare.

Men: MedlinePlus says it “also rarely affects men”. According to the WHO about 99% of breast cancers occur in women and about 0.5% to 1% in men, and the NCI states that fewer than 1 in 100 cases in the United States occur in men. The NHS says: “Anyone can get breast cancer”.

Figures according to the WHO: about 2.4 million women were diagnosed with it in 2024 and about 694,000 died worldwide, and it was the most common cancer in women in 164 of 186 countries. It occurs in every country of the world in women at any age after puberty, with rates rising at older ages. The WHO notes a difference between countries: in countries with a very high Human Development Index, 1 in 12 women is diagnosed in her lifetime and 1 in 71 dies, while in low-index countries 1 in 27 women is diagnosed and 1 in 48 dies. An NCI page states that it is the second most common cancer in women after skin cancer.

Causes

The NHS says: “Anyone can get breast cancer, and it is not always clear what causes it”. The WHO states that about 80% of breast cancers arise in women who have no modifiable risk factor other than sex (female) and age (over 40), and that female sex is the strongest risk factor.

Genetics: inherited changes (mutations) in certain genes such as BRCA1 and BRCA2 raise the risk of breast and ovarian cancer (CDC, NCI). MedlinePlus lists genetic tests such as BRCA and TP53 among the possible tests.

Risk factors

Factors that cannot be changed according to the CDC: advancing age (“most breast cancers are diagnosed after age 50”), gene mutations such as BRCA1 and BRCA2, starting periods early and reaching menopause late (longer exposure to hormones), dense breasts, previous breast cancer, family history, radiation therapy to the chest or breast before age 30, and exposure to the drug DES. The NCI says the most important risk factor after female sex is advancing age, and that dense breasts raise the risk and make cancer harder to detect on a mammogram.

Factors that can be changed according to the CDC and NCI: physical inactivity, being overweight or obese, especially after menopause, combined hormone replacement therapy (oestrogen with progesterone), a first pregnancy after age 30, not breastfeeding or never completing a pregnancy, and alcohol (“the more alcohol you drink, the higher the risk”). The WHO adds tobacco use.

The NHS adds: age over 50, certain breast conditions (benign breast disease, ductal carcinoma in situ and lobular carcinoma in situ), higher hormone levels, starting periods before age 12 or reaching menopause after 55, never having children or a first birth after 30, use of the contraceptive pill in the last 10 years or hormone replacement therapy, and smoking. These factors do not mean that getting the disease is inevitable.

In men according to the NCI: previous radiation treatment to the chest, inherited changes in BRCA1 or BRCA2, conditions that raise oestrogen such as Klinefelter syndrome, and having one or more female relatives who had breast cancer.

Symptoms

Signs according to the CDC: a new lump in the breast or armpit, thickening or swelling of part of the breast, irritation or dimpling of the breast skin, redness or flaking in the nipple area or breast, the nipple turning inward or pain in its area, discharge from the nipple other than milk including blood, any change in the size or shape of the breast, and pain in any area of the breast.

The WHO describes the lump or thickening as “often painless”, and lists a change in the appearance of the nipple or skin around it and abnormal or bloody fluid from it. The NHS lists a lump or swelling in the breast, chest or armpit, a change in the colour of the breast skin, and nipple discharge (if you are not pregnant or breastfeeding), and notes that “breast pain alone is not usually a symptom of breast cancer”.

These symptoms may occur with non-cancerous conditions, and “most breast lumps are caused by other medical conditions” such as fibrocystic changes and cysts (CDC). The NHS says that having symptoms does not necessarily mean you have the disease, but it is important to be checked by a doctor. In men, a lump or thickening in or near the breast is the most common sign (NCI).

How is it diagnosed?

According to the NHS, tests at a breast clinic include: an examination of the breasts, X-ray imaging of the breast (mammogram), ultrasound, and taking a small sample of cells (biopsy), usually with a needle; the biopsy is examined to confirm cancer and to look for certain proteins in its cells that help choose the most suitable treatment.

MedlinePlus lists: clinical examination and medical history, mammography, ultrasound, MRI, breast biopsy, a blood chemistry panel, genetic tests (BRCA and TP53), the HER2 test, oestrogen and progesterone receptor tests, and sentinel lymph node biopsy to determine the stage. The CDC says doctors test breast cancer cells to find out whether they carry these receptors and the protein.

After diagnosis, imaging such as a CT scan, MRI or positron emission tomography (PET) and blood tests may be requested to find the extent of spread, the type of cancer and whether it is caused by changes in genes (NHS). The WHO describes the stages: spread to the lymph nodes (stages II or III) or to other parts of the body (stage IV).

Screening: the WHO defines it as applying mammography to people who appear healthy, “usually women aged 50 to 69”, to detect lesions before symptoms appear. The CDC reports that the US Preventive Services Task Force (USPSTF) recommends that average-risk women aged 40 to 74 have a mammogram every two years, that different recommendations may apply to those at higher risk, and that MRI is used with mammography to screen high-risk women. The NHS advises attending screening when you are invited. Screening programmes, their ages and their intervals differ between countries, and your doctor decides what suits you.

Benefits and harms of screening according to the NCI and CDC: it allows cancer to be detected before symptoms so treatment starts early, but harms include false-positive results and the tests and anxiety that follow, overdiagnosis that may lead to unnecessary treatment, and radiation exposure. The NCI says: “Even if your last mammogram was normal, tell your doctor if you feel something unusual”.

Treatment

The treatment categories usually used are listed here; this is not a prescription. The doctor chooses the plan according to each person's condition; do not change any medicine or dose without a specialist.

How treatment is chosen: according to the WHO it depends on the cancer's subtype and extent of spread, and medicines are chosen according to the tumour's biological characteristics as determined by special tests. The NHS says it depends on the size, type, location and spread of the cancer and on general health. The NCI says: “You and your cancer care team will work together to decide on a treatment plan”. The plan is determined by the doctor with the patient.

Local treatments (NCI): they target the area of the cancer rather than the whole body. Surgery is “usually the main treatment” (NHS): removing only the affected part (breast-conserving surgery) or removing the whole breast (mastectomy), and the lymph nodes in the armpit may be removed; a sentinel lymph node biopsy is usually done during surgery or separately (NCI). Radiotherapy kills cancer cells and may be given after surgery to reduce the chance of recurrence. (See general surgery.)

Systemic treatments (reaching cancer cells throughout the body): chemotherapy may be given before or after surgery or for secondary cancer, and “not all breast cancer patients get chemotherapy” (NCI). Hormone therapy lowers the amount of certain hormones or stops them reaching cancer cells (NHS), and lowers the risk of recurrence in certain types (NCI); the WHO states that these medicines are taken for years and lower the chance of recurrence of “hormone-positive” cancers by about half. Targeted drugs kill cancer cells, and immunotherapy helps the immune system kill cancer and may be used for triple-negative breast cancer (NHS, NCI). (See oncology.)

Breast reconstruction: after a mastectomy, reconstruction can be chosen, in which the surgeon makes a new breast, at the same time or in a later operation (NHS). The NCI mentions two methods: implants (saline or silicone) or the person's own tissue from the abdomen, back, thigh or buttocks, and calls reconstruction immediate or delayed. MedlinePlus says “a plastic surgeon can help you make the decision”. (See plastic and reconstructive surgery.)

Breast cancer in men is “usually treated in the same way” as in women, but mastectomy is used more often in them than breast-conserving surgery (NCI). Do not start or stop any medicine without your medical team; the team explains the treatments, their benefits and side effects and works with you on the plan (NHS).

Follow-up

The NHS says: “You will have regular check-ups during and after any treatment, and may have tests and scans”, and a specialist clinical nurse is the main point of contact during and after treatment. People who have had breast cancer before are more likely to get it a second time (CDC), so any new change is worth reviewing even after a normal mammogram (NCI). This page does not cover detailed follow-up schedules.

Complications

Spread: invasive cancer may spread to nearby lymph nodes or other organs (WHO), and when it reaches other parts of the body through the lymph nodes or blood it is called metastatic breast cancer (CDC). Radiotherapy and chemotherapy are also used to treat secondary cancer or its symptoms (NHS).

Each treatment has side effects that the treating team explains (NHS), and the NCI indicates there are risks of lumpectomy and mastectomy without detailing them in the source page. This page does not cover the side effects of treatment in detail.

Prevention

To reduce risk the NHS lists: reducing alcohol, losing weight if overweight, quitting smoking, and discussing the contraceptive pill or hormone replacement therapy with the doctor. MedlinePlus lists healthy lifestyle changes, limiting alcohol and regular mammography, which may detect cancer in its early stages “when it is easier to treat”.

For those at higher risk (such as BRCA mutation carriers or a strong family history) the CDC advises talking to the doctor about screening and ways to reduce risk, such as medicines that block or lower oestrogen, or surgery; MedlinePlus mentions preventive medicines or surgery for high-risk women. This is a decision made only with the doctor. Since most cases occur without a modifiable risk factor (WHO), attention to symptoms and screening according to your country's programme remain important.

Living with it

The NCI says the patient and the cancer care team decide the plan together, and the NHS lists a team of specialists with a specialist clinical nurse who is the main point of contact. The WHO stresses that early diagnosis linked with comprehensive treatment, rehabilitation and palliative care is essential to preserve the best function and well-being. This page does not cover life after breast cancer.

Common questions