Breast Cancer: Subtypes, Biomarkers, Stages & Treatment

Breast cancer begins in the cells of the breast, most often in the milk ducts (ductal carcinoma) or the milk-producing lobules (lobular carcinoma). It can remain confined to the breast and nearby lymph nodes (localised or regional disease) or spread through the bloodstream or lymphatic system to distant organs such as bone, liver, lung, or brain, at which point it is described as metastatic or stage IV disease.

Not all breast cancers behave the same way. Two tumours that look similar under the microscope can grow at very different speeds and respond to completely different treatments, depending on their underlying molecular features. This is why every newly diagnosed breast cancer is tested for a specific set of biomarkers before a treatment plan is finalised.

The disease can also begin as a non-invasive, pre-cancerous change called ductal carcinoma in situ (DCIS), where abnormal cells are confined to the ducts and have not invaded surrounding tissue. DCIS is highly treatable, though it requires management to reduce the chance of progression to invasive cancer.

Breast cancer affects women overwhelmingly more often than men, but male breast cancer does occur and is managed with broadly similar principles, adapted to differences in anatomy and hormone biology.

Globally, breast cancer is the most frequently diagnosed cancer among women, and awareness of both risk factors and early warning signs plays an important role in finding the disease at a stage when treatment is most effective.

A breast cancer diagnosis raises many questions, but treatment today is highly personalised, based on the specific biology of your tumour rather than a one-size-fits-all approach. Two people with the same stage of breast cancer may receive quite different treatment plans if their receptor status or genetic profile differs.

Discussing your specific pathology results — including ER, PR, and HER2 status, tumour grade, and any genomic or genetic testing — with your oncology team will clarify which therapies are most likely to help you and what monitoring plan makes sense going forward. It is normal to need time to process this information, and most centres offer nurse navigators, counselling, or patient support services to help.

The most common sign of breast cancer is a new lump or area of thickening in the breast or underarm, which is often, though not always, painless. Other warning signs include a change in the size, shape, or contour of the breast, dimpling or puckering of the skin (sometimes described as looking like an orange peel), redness or scaling of the skin, and nipple changes such as inversion, discharge, or crusting.

Inflammatory breast cancer, a less common but more aggressive form, can present with rapid swelling, warmth, and redness of the breast without a distinct lump, and can be mistaken for infection, so persistent symptoms should always be evaluated.

Many early-stage breast cancers cause no noticeable symptoms at all and are detected only through screening mammography, which is one of the main reasons regular screening is recommended for people in the relevant age and risk groups.

Any new or persistent breast change — a lump, skin change, or nipple abnormality — should be evaluated promptly by a clinician, even though most breast changes, particularly in younger people, turn out to be benign.

Breast cancer develops when genetic changes accumulate in breast cells, disrupting the normal controls over cell growth, division, and death. Most of these changes are acquired over a lifetime (somatic mutations) rather than inherited, arising from a combination of hormonal exposure, ageing, and chance errors in cell division.

Oestrogen and progesterone, the hormones that regulate the menstrual cycle and breast tissue development, can promote the growth of hormone receptor-positive tumours, which is part of why lifetime hormonal exposure — including age at first period, age at menopause, and use of hormone therapy — influences risk.

In a smaller proportion of cases, an inherited mutation in a gene such as BRCA1, BRCA2, PALB2, TP53, or PTEN substantially raises lifetime risk and can also influence tumour biology, since BRCA-related cancers are more likely to be triple-negative and to respond to specific drug classes.

Ultimately, no single cause explains most breast cancers; it typically reflects the interaction of genetic background, hormonal history, environmental exposures, and simple biological chance.

Non-modifiable risk factors include being female, increasing age, a personal or family history of breast or ovarian cancer, inherited mutations in genes such as BRCA1/BRCA2, dense breast tissue, and early first menstruation or late menopause, all of which extend lifetime hormonal exposure.

Modifiable factors that can influence risk include excess body weight after menopause, physical inactivity, alcohol consumption, and long-term use of combined hormone replacement therapy after menopause. Having children later in life or not breastfeeding is associated with a modestly higher risk compared with earlier childbirth and breastfeeding, though these are personal decisions influenced by many factors beyond cancer risk.

It is important to note that most people diagnosed with breast cancer have no strong family history and no single identifiable cause; risk factors describe probabilities across populations, not certainties for any individual. People with a strong family history, especially involving breast or ovarian cancer at a young age, or with known ancestry associated with higher rates of BRCA mutations, may be candidates for genetic counselling and earlier or more intensive screening.

Diagnosis typically begins with a clinical breast examination and imaging, most commonly mammography, sometimes supplemented with ultrasound or MRI, particularly in younger patients or those with dense breast tissue. Imaging that raises suspicion of cancer is followed by a core needle biopsy, which removes a small tissue sample for examination under the microscope and biomarker testing.

Once cancer is confirmed by biopsy, the pathology report will describe the histological type (such as invasive ductal or lobular carcinoma), tumour grade (how abnormal the cells look and how quickly they are likely to grow), and receptor status (ER, PR, HER2).

Depending on the initial findings, further imaging such as breast MRI, CT scan, bone scan, or PET scan may be used to determine whether the cancer has spread beyond the breast and regional lymph nodes, a process called staging. Not every patient needs every test; the extent of staging work-up is guided by tumour size, grade, and symptoms.

A sentinel lymph node biopsy, performed at the time of surgery, is often used to check whether cancer cells have spread to the lymph nodes under the arm, which is an important factor in both staging and treatment planning.

Breast cancer is staged using the TNM system, which considers tumour size and extent (T), whether nearby lymph nodes are involved (N), and whether the cancer has spread to distant organs (M). These are combined, along with biomarker results in current staging systems, into an overall stage from 0 to IV.

Stage 0 refers to non-invasive disease such as DCIS, confined to the ducts. Stages I to III describe cancer that is invasive but has not spread beyond the breast and nearby lymph nodes, with increasing tumour size or nodal involvement as the stage number rises. Stage IV, or metastatic breast cancer, means the cancer has spread to distant sites such as bone, liver, lungs, or brain.

Modern staging for breast cancer also incorporates tumour grade and biomarker status (ER, PR, HER2) alongside anatomical extent, because these factors meaningfully affect prognosis and can shift the overall stage grouping compared with anatomy alone.

Stage at diagnosis remains one of the strongest predictors of outcome and is central to deciding whether treatment aims for cure (localised and regional disease) or long-term control (metastatic disease), though biology increasingly refines these decisions within each stage.

Every invasive breast cancer diagnosis includes biomarker testing on the biopsy sample for oestrogen receptor (ER), progesterone receptor (PR), and HER2 status, usually performed by immunohistochemistry and, when HER2 results are unclear, confirmed with in-situ hybridisation (such as FISH). These results define whether a tumour is hormone receptor-positive, HER2-positive, or triple-negative.

For many patients with early-stage, hormone receptor-positive, HER2-negative breast cancer, a multigene genomic expression test can be performed on the tumour tissue to estimate the risk of recurrence and help decide whether adding chemotherapy to endocrine therapy is likely to provide meaningful benefit.

Germline genetic testing, usually via a blood or saliva sample, may be offered to assess inherited mutations in BRCA1, BRCA2, PALB2, and other genes, based on factors such as age at diagnosis, tumour subtype (especially triple-negative disease), and family history. A positive result can open eligibility for PARP inhibitor therapy and has implications for family members.

In advanced or metastatic disease, additional testing such as PIK3CA, ESR1, or other genomic alterations may be assessed, often through tumour tissue or blood-based liquid biopsy, to identify additional targeted treatment options as the disease evolves.

Breast cancer is broadly classified into three clinically important subtypes: hormone receptor-positive (ER and/or PR positive), HER2-positive, and triple-negative, each with distinct biology, prognosis, and treatment pathways. Hormone receptor-positive, HER2-negative disease is the most common subtype overall and is generally treated with endocrine therapy as a backbone of care.

Invasive ductal carcinoma, arising from the milk ducts, is the most common histological type, accounting for the majority of invasive breast cancers, followed by invasive lobular carcinoma, which arises from the milk-producing lobules and can be more difficult to detect on standard mammography.

Less common forms include inflammatory breast cancer, an aggressive subtype presenting with skin changes rather than a discrete lump, and Paget disease of the nipple, which involves the skin of the nipple and areola and is often associated with an underlying ductal carcinoma.

A subset of cases, more common in younger patients and those with triple-negative or HER2-positive disease, arise in the setting of an inherited mutation such as BRCA1 or BRCA2, which can influence both prognosis and eligibility for specific targeted therapies.

Treatment for early-stage breast cancer typically combines local therapy — surgery, either breast-conserving surgery (lumpectomy) followed by radiotherapy, or mastectomy — with systemic therapy tailored to the tumour's biomarker profile. Hormone receptor-positive tumours are usually treated with endocrine therapy, often for five to ten years, sometimes combined with CDK4/6 inhibitors in higher-risk cases; chemotherapy may be added based on tumour size, grade, nodal status, and genomic risk-score results.

HER2-positive breast cancer is treated with HER2-targeted therapies such as trastuzumab, often combined with chemotherapy and, in some cases, a second HER2-targeted agent, both before and after surgery depending on tumour size and response.

Triple-negative breast cancer, which lacks hormone receptor and HER2 targets, is generally treated with chemotherapy, and immunotherapy with a checkpoint inhibitor has become part of standard care for many patients with higher-risk early-stage or advanced triple-negative disease. PARP inhibitors are an option for patients with BRCA1/BRCA2 mutations in certain settings.

Radiotherapy is commonly used after breast-conserving surgery, and sometimes after mastectomy, to reduce the risk of local recurrence, targeting the breast, chest wall, or regional lymph nodes depending on individual risk factors.

Metastatic breast cancer is managed with a sequence of systemic therapies selected according to subtype: endocrine therapy with targeted agents such as CDK4/6 inhibitors for hormone receptor-positive disease, continued HER2-targeted therapy for HER2-positive disease, and chemotherapy, immunotherapy, or antibody-drug conjugates for triple-negative or heavily pretreated disease. The goal shifts from cure to controlling the cancer, relieving symptoms, and preserving quality of life for as long as possible.

Supportive care, including management of treatment side effects, bone health (particularly important with endocrine therapy and bone metastases), fertility preservation counselling for younger patients, and psychological support, is an integral part of breast cancer care at every stage.

Survival statistics for breast cancer are generally favourable compared with many other cancers, particularly when detected early, but they are population averages and cannot predict any individual's outcome. According to data such as that compiled by the U.S. SEER programme, the overall 5-year relative survival for breast cancer diagnosed at a localised stage is approximately 99%, dropping to roughly 87% for regional-stage disease (spread to nearby lymph nodes), and to approximately 32% for distant-stage (metastatic) disease at diagnosis.

These figures vary considerably depending on tumour subtype, grade, biomarker status, and how well the cancer responds to treatment; for instance, outcomes for HER2-positive and triple-negative disease have improved substantially in recent years with the introduction of targeted therapies and immunotherapy, and older survival statistics may not fully reflect current treatment options.

Even within metastatic disease, survival can range widely; some patients live for many years with good quality of life while managing their cancer as a chronic condition through sequential lines of treatment, particularly with hormone receptor-positive or HER2-positive subtypes.

Your oncologist is best placed to discuss what published statistics may or may not mean for your specific situation, taking into account your tumour's characteristics, overall health, and response to treatment so far.