What is Breast Cancer?
Breast cancer occurs when cells in the breast grow abnormally and form a tumour that can invade nearby tissue or spread elsewhere. The most common sign is a new painless lump, but changes in skin, nipple, or breast shape also matter. Screening mammography is recommended every other year from age 40 to 74 under current USPSTF guidance.
Key takeaways
- A new lump is the most common sign, but skin dimpling, nipple change, and unusual discharge also warrant evaluation.
- USPSTF now recommends biennial screening mammography starting at age 40 for women at average risk.
- Subtype matters enormously: hormone receptor and HER2 status determine which treatments will work.
- Most breast lumps are benign, but any new lump should be evaluated rather than watched indefinitely.
- Men can develop breast cancer too, and their diagnosis is often delayed because it is not expected.
Overview
Breast cancer is the most commonly diagnosed cancer in women worldwide, and outcomes have improved substantially over the past three decades through a combination of earlier detection and far better treatment. It begins most often in the cells lining the milk ducts, less often in the lobules that produce milk. Some tumours remain confined to the duct — ductal carcinoma in situ — while invasive cancers grow through into surrounding breast tissue and can spread to lymph nodes and beyond.
What determines treatment today is far more than size and spread. Hormone receptor status, HER2 status, and increasingly genomic profiling define biologically distinct diseases that respond to entirely different therapies, and the same tools now help identify people who can safely avoid chemotherapy altogether. That is why two people with apparently similar tumours may receive very different treatment plans, and why molecular testing of the biopsy sample is standard rather than optional. It is also why a diagnosis alone tells you very little until those results are back — a wait that is often the hardest part.
What Breast Cancer is
Breast cancers are classified by what drives them. Hormone receptor positive tumours — expressing estrogen and often progesterone receptors — make up the majority and respond to endocrine therapy. HER2-positive tumours overexpress a growth-signalling protein and respond to HER2-targeted antibodies and related drugs. Triple-negative breast cancer lacks all three targets, tends to be more aggressive, and is treated primarily with chemotherapy and, increasingly, immunotherapy.
Ductal carcinoma in situ is non-invasive disease confined to the duct; it is not life-threatening in itself but is treated because a proportion would progress. Inflammatory breast cancer is a rare aggressive form presenting with redness, warmth, and skin thickening rather than a lump — it is often mistaken for infection and needs urgent specialist assessment.
Common symptoms
Any new, persistent change in a breast deserves evaluation, even though most changes turn out to be benign.
- A new lump or thickening in the breast or armpit, often painless and firm
- Change in breast size or shape
- Skin dimpling or puckering, sometimes described as resembling orange peel
- Nipple retraction — a nipple turning inward that previously did not
- Spontaneous nipple discharge, particularly if bloody or from one duct
- Redness, scaling, or crusting of the nipple or areola
- Persistent breast or armpit pain in one specific area
Less common symptoms
- Swelling of all or part of the breast without a distinct lump
- Warmth and rapid redness spreading across the breast — possible inflammatory breast cancer requiring urgent assessment
- Swollen lymph nodes in the armpit or above the collarbone
- Bone pain, breathlessness, or persistent headache — possible signs of spread
- A lump in a man's breast, usually just behind the nipple
Risk factors
- Female sex and increasing age — the two strongest risk factors overall
- Inherited mutations such as BRCA1, BRCA2, and PALB2 — high individual risk warranting specialist management
- Family history of breast or ovarian cancer, especially at a young age or in multiple relatives
- Personal history of breast cancer or of certain high-risk benign changes such as atypical hyperplasia
- Dense breast tissue — raises risk and reduces mammogram sensitivity
- Lifetime estrogen exposure — early first period, late menopause, first pregnancy after 30, no pregnancies, or several years of combined menopausal hormone therapy
- Alcohol — risk rises with the amount consumed, with no clear safe threshold
- Excess weight after menopause and physical inactivity
- Previous chest radiotherapy, particularly before age 30
Causes
Breast cancer arises from accumulated genetic damage in breast cells. Most of this damage is acquired over a lifetime, influenced by hormonal exposures, alcohol, body weight after menopause, and chance. Estrogen drives proliferation in hormone-sensitive tissue, which explains why the number of menstrual cycles over a lifetime, timing of pregnancy, and hormone therapy all shift risk.
Inherited mutations account for roughly 5-10% of cases. BRCA1 and BRCA2 are the best known, and identifying them changes screening intensity, informs risk-reducing surgery decisions, opens access to specific targeted therapies, and has implications for relatives. Most people diagnosed with breast cancer, however, have no family history at all.
How it is diagnosed
Assessment usually follows a triple approach: clinical examination, imaging, and tissue sampling.
| Test or assessment | What it looks at |
|---|---|
| Screening mammography | Low-dose X-ray imaging of the breast. USPSTF recommends screening every other year from age 40 to 74 for women at average risk; some organisations recommend annual screening from 40. |
| Diagnostic mammography and ultrasound | Focused imaging of a specific area of concern. Ultrasound is particularly useful in dense breasts and for distinguishing cysts from solid masses. |
| Breast MRI | Used for supplemental screening in people at high inherited risk, for assessing extent of disease, and for evaluating response to pre-surgical treatment. |
| Core needle biopsy | The definitive diagnostic step, taking a tissue sample under imaging guidance to confirm cancer and determine subtype. |
| Receptor and molecular testing | Estrogen receptor, progesterone receptor, HER2 status, and proliferation markers on the biopsy sample determine which treatments will be effective. |
| Staging and genomic assays | Lymph node assessment, imaging where indicated, and multigene recurrence assays that help decide whether chemotherapy adds benefit in early hormone-positive disease. |
Treatment overview
Treatment is highly individualized by subtype, stage, and personal preference, and is planned by a multidisciplinary team. The categories below describe modalities; all specific regimens and dosing are set by the oncology team.
Surgery
Breast-conserving surgery (lumpectomy) with radiation, or mastectomy, with sentinel lymph node biopsy to assess spread. Survival is equivalent between the two approaches in appropriately selected early cancers.
Radiation therapy
Given after breast-conserving surgery and after mastectomy in higher-risk cases, to reduce local recurrence.
Endocrine (hormone) therapy
Tamoxifen, aromatase inhibitors, and ovarian suppression for hormone receptor positive disease, typically continued for five to ten years.
HER2-targeted therapy
Antibodies and antibody-drug conjugates directed at HER2, which transformed outcomes for HER2-positive breast cancer.
Chemotherapy
Used before or after surgery depending on subtype and stage, and central to triple-negative disease. Genomic assays help avoid it where it adds little.
Immunotherapy and targeted agents
Checkpoint inhibitors in certain triple-negative cancers, CDK4/6 inhibitors in advanced hormone-positive disease, and PARP inhibitors for BRCA-associated cancers.
Reconstruction and survivorship care
Breast reconstruction options, lymphedema prevention, bone health monitoring on aromatase inhibitors, fertility discussion, and psychological support.
Lifestyle considerations
- Attend screening mammography at the interval recommended for you.
- Become familiar with how your breasts normally look and feel, and report changes rather than waiting for the next scheduled screen.
- Limit alcohol — the association with breast cancer risk is consistent and dose-related.
- Stay physically active; regular activity is associated with lower risk and better outcomes after diagnosis.
- Maintain a healthy weight, particularly after menopause.
- Breastfeed if you are able and choose to; it is associated with a modest reduction in risk.
- Discuss the risks and benefits of menopausal hormone therapy individually rather than assuming either extreme.
- Know your family history on both sides and share it with your clinician.
Prevention
- Attend screening at the recommended interval — early detection substantially improves outcomes.
- Limit alcohol intake.
- Maintain a healthy weight and stay physically active, especially after menopause.
- Discuss genetic counselling if you have a strong family history of breast, ovarian, pancreatic, or prostate cancer.
- For those at high risk, discuss risk-reducing medication such as tamoxifen or aromatase inhibitors, and risk-reducing surgery where appropriate.
- Use menopausal hormone therapy at the lowest useful duration if you need it, with an individual risk discussion.
Warning signs and when to get help
Signs that need emergency care
If you believe you are experiencing a medical emergency, call emergency services immediately (911 in the United States).
- Rapidly spreading breast redness, swelling, and warmth with skin thickening — possible inflammatory breast cancer or serious infection, seek same-day care
- Sudden severe breathlessness or chest pain during or after treatment — call emergency services
- Fever above 100.4°F (38°C) while receiving chemotherapy — possible neutropenic sepsis, seek emergency care immediately
- Sudden severe back pain with leg weakness or bladder changes — possible spinal cord compression
- New confusion, seizure, or sudden severe headache
Signs that warrant a prompt appointment
These are not emergencies, but they are worth a call to your clinician rather than a wait-and-see.
- Any new breast lump or thickening that persists through a menstrual cycle
- Nipple retraction, skin dimpling, or persistent scaling of the nipple
- Spontaneous, especially bloody, nipple discharge
- A new lump in the armpit or above the collarbone
- Persistent bone pain, unexplained weight loss, or persistent cough after treatment
- Arm swelling, heaviness, or tightness after lymph node surgery
Questions to ask a healthcare professional
Take these to your next appointment — or build an agenda with the Appointment Prep tool.
- What subtype is my cancer — hormone receptor and HER2 status?
- What stage is it, and what does that mean for my treatment options?
- Is breast-conserving surgery an option for me, and how does it compare to mastectomy?
- Would a genomic recurrence assay help decide whether I need chemotherapy?
- Should I have genetic testing, and what would it mean for my family?
- What are the likely short and long-term effects of the treatments you are recommending?
- What should I know about fertility, menopause, or bone health with this treatment?
- What does follow-up look like after treatment ends?
Frequently asked questions
At what age should I start mammograms?
The USPSTF recommends screening mammography every other year from age 40 through 74 for women at average risk. Some organisations recommend annual screening beginning at 40. If you have a strong family history or a known genetic mutation, screening usually starts earlier and may include MRI.
Are most breast lumps cancer?
No — the majority are benign, including cysts and fibroadenomas, particularly in younger women. That said, a new lump cannot be distinguished reliably by feel alone, so it should be evaluated rather than monitored indefinitely at home.
Does dense breast tissue matter?
Yes, in two ways. Dense tissue is itself associated with somewhat higher risk, and it makes mammograms harder to read because both dense tissue and tumours appear white. Many people with dense breasts are offered supplemental imaging — discuss options with your clinician.
Does alcohol increase breast cancer risk?
Yes, and the association is consistent and dose-related, with no clearly safe threshold identified. Even modest regular intake is associated with a measurable increase, so reducing alcohol is one of the more actionable prevention steps.
Can men get breast cancer?
Yes. It is uncommon — roughly 1% of cases — but men have breast tissue and can develop the same disease. Diagnosis is often later because it is unexpected, so any new lump behind the nipple in a man should be evaluated.
Do antiperspirants or bras cause breast cancer?
No. Studies have not found a link between breast cancer and antiperspirant use, underwire bras, or breast implants causing the common types of breast cancer. Established risk factors are age, genetics, hormonal history, alcohol, weight, and activity.
Sources
- American Cancer Society — Breast Cancer — Signs, screening, subtypes, and treatment overview
- NCI — Breast Cancer — NIH staging, treatment, and genetics information
- USPSTF — Breast Cancer: Screening — Biennial screening recommendation from age 40 to 74
- CDC — Breast Cancer — US screening programs and risk-factor summary
- MedlinePlus — Breast Cancer — Consumer summary and related tests
Health Captain links to primary public-health and clinical sources so you can read the original material yourself. See our sources policy.