The short answer: breast cancer is a disease in which abnormal cells in the breast grow out of control and form tumours [9]. It most often starts in the milk ducts or the milk-producing lobules [9]. It is the most common cancer among women worldwide, with about 2.3 million new cases and 670,000 deaths in 2022 [9]. Men can get breast cancer too, though it is rare, accounting for 0.5 to 1 percent of all cases [9]. Treatment usually involves surgery and often includes radiation, chemotherapy, hormone therapy, or targeted drugs [1][3].
Breast cancer is not a single disease. It is a group of conditions that differ in how they start, how they behave, and how they respond to treatment [3]. This article explains what is documented about the causes, symptoms, and treatment options, and separates facts from common myths.
What causes breast cancer?
Doctors do not know exactly what causes each case of breast cancer. However, research has identified several factors that increase the risk [2][9].
The most important risk factor is being female. Approximately 99 percent of breast cancers occur in women [9]. Age is the second strongest factor. The risk increases with age, and more than three-quarters of women who get breast cancer are over 50 [6].
There are two broad categories of risk: factors you cannot change and factors you can [10][18].
Risk factors you cannot change
- Inherited gene mutations. About 5 to 10 percent of breast cancers are linked to inherited gene changes [6][18]. The most well-known are BRCA1 and BRCA2. Women with these mutations have a lifetime risk of up to 72 percent or higher [14]. Other high-risk genes include PALB2, TP53, PTEN, and CDH1 [2][14].
- Family history. Having a mother, sister, or daughter with breast cancer increases your risk [1][6].
- Personal history. If you have had cancer in one breast, you are at higher risk of developing it in the other breast [6][18].
- Reproductive history. Starting periods before age 12, starting menopause after age 55, having a first child after age 30, or never having children all slightly increase risk [6][10][18].
- Dense breast tissue. Having more glandular and fibrous tissue and less fatty tissue increases risk and also makes mammograms harder to read [5][18].
- Radiation exposure. Chest radiation at a young age, especially between ages 10 and 14, increases risk [5][6].
Risk factors you can change
- Alcohol consumption. Regularly drinking alcohol increases risk. Experts recommend limiting to one drink per day [5][10].
- Obesity after menopause. Excess fat tissue raises estrogen levels and increases risk [5][10][18].
- Lack of exercise. Physical activity helps maintain a healthy weight and may lower risk [10][18].
- Smoking. Smoking is linked to increased breast cancer risk and many other cancers [5][10].
- Hormone therapy. Long-term use of combined estrogen and progestin after menopause increases risk [5][6][10].
What is myth, not documented
Myth: Breast cancer is caused by stress or wearing tight bras. There is no reliable scientific evidence that psychological stress or bra use causes breast cancer. These claims are not supported by the research [2].
Myth: Only women with a family history get breast cancer. Most women diagnosed with breast cancer have no known family history of the disease [9]. The absence of a family history does not mean low risk.
Symptoms of breast cancer
Breast cancer often causes no symptoms in its early stages. This is why screening is important [11]. When symptoms do appear, the most common first sign is a painless lump in the breast [1][9].
Other documented symptoms include [7][9][15]:
- A lump or thickening in the breast, chest, or armpit
- A change in the size, shape, or feel of the breast
- Skin changes such as dimpling, puckering, or redness
- Skin that looks like the peel of an orange
- A change in the nipple, such as turning inward (inverted nipple)
- Nipple discharge, which may be bloody, when not pregnant or breastfeeding
- A rash or scaly skin on the nipple
- Breast or armpit pain (though pain alone is not usually a sign of cancer)
On brown or black skin, redness may look darker or more reddish-brown than on white skin [7][15].
If breast cancer has spread to other parts of the body, symptoms depend on where it has gone. It most commonly spreads to the bones, liver, lungs, or brain. This can cause bone pain, headaches, or other problems [9][15].
How breast cancer is diagnosed and staged
If you have symptoms or an abnormal screening result, doctors use several tests. These include mammogram, ultrasound, and sometimes MRI. A biopsy is needed to confirm cancer [1][3].
Once cancer is diagnosed, it is assigned a stage from 0 to IV [3]. Staging reflects how far the cancer has spread.
| Stage | What it means |
|---|---|
| Stage 0 | Cancer is in situ, meaning it has not invaded surrounding tissue [3] |
| Stages I to III | Cancer has spread to tissues within or near the breast (localised or regional) [3] |
| Stage IV | Cancer has spread to distant organs (metastatic) [3] |
Doctors also test the cancer cells for hormone receptors (estrogen and progesterone) and HER2 protein. These markers guide treatment decisions [3].
Treatment options
Treatment depends on the stage, type, and receptor status of the cancer, as well as the patient’s preferences [3][4].
Surgery
Surgery is the main treatment for most breast cancers. There are two main options [3]:
- Breast-conserving surgery removes the tumour and some surrounding tissue, usually followed by radiation therapy.
- Mastectomy removes the whole breast. Reconstruction can often be done at the same time.
Lymph nodes in the armpit are often checked to see if cancer has spread there [3].
Radiation therapy
Radiation uses high-energy rays to kill cancer cells. It is commonly used after breast-conserving surgery to reduce the risk of recurrence [3][4]. Newer schedules called hypofractionated and ultra-hypofractionated radiation deliver the same or better results in fewer sessions, and the 2025 St Gallen consensus endorsed these for more patients [4].
Systemic treatments
These are drugs that travel through the body to reach cancer cells anywhere. They include [3][4]:
- Chemotherapy: Kills fast-growing cells. Used for many types of breast cancer, especially triple-negative.
- Hormone therapy: Blocks hormones that fuel hormone-receptor-positive cancers. Examples include tamoxifen and aromatase inhibitors.
- Targeted therapy: Attacks specific features of cancer cells. For HER2-positive cancer, drugs like trastuzumab are used.
- Immunotherapy: Helps the immune system fight cancer. Used for triple-negative breast cancer.
- CDK4/6 inhibitors: Newer drugs like abemaciclib and ribociclib are used for some high-risk hormone-receptor-positive cancers [4][20].
The 2025 St Gallen consensus update
An international panel of experts updates breast cancer treatment recommendations every two years. The 2025 consensus included several important changes [4]:
- Endorsement of shorter radiation schedules for more patients
- Recommendation for platinum-based chemotherapy in triple-negative breast cancer
- Avoiding sentinel lymph node surgery in many low-risk ER-positive cancers
- Use of immunotherapy in triple-negative and some ER-low-positive tumours
- Guidance on re-irradiation and systemic therapy for local recurrence
- Focus on survivorship, including minimising neuropathy and addressing sexual health concerns
The bottom line
Breast cancer is a complex disease with many types, causes, and treatment options. Being female and getting older are the strongest risk factors, but lifestyle factors like alcohol use and obesity also play a role. Early detection through awareness and screening saves lives. Treatment is increasingly personalised, based on the specific biology of the tumour. The 2025 international guidelines reflect a shift toward more precise, less invasive care that considers the whole patient.
Disclaimer
This article is for informational purposes only and is not a substitute for professional medical advice. If you notice any breast changes or have concerns about your risk, consult a qualified healthcare provider. We welcome your feedback and corrections. Please contact us if you notice any errors.
References
- [1] Breast Cancer, MSD Manual Consumer Version
- [2] Breast Cancer Risk and Prevention, American Cancer Society
- [3] Breast Cancer, MSD Manual Consumer Version
- [4] Tailoring treatment to cancer risk and patient preference: the 2025 St Gallen International Breast Cancer Consensus Statement, Annals of Oncology
- [5] Breast Cancer, Merck Manual Consumer Version
- [6] About breast cancer, New York State Department of Health
- [7] Symptoms of breast cancer, Cancer Research UK
- [9] Breast cancer, World Health Organization
- [10] Causes & Risk Factors, SingHealth
- [11] Breast Cancer: Symptoms, University of Rochester Medical Center
- [14] Breast cancer, National Cancer Institute
- [15] Symptoms of breast cancer in women, NHS UK
- [18] Breast Cancer Risk Factors, UCSF Breast Care Center
- [20] Brystkreft – handlingsprogram, Den norske legeforening
