Breast Cancer
Breast cancer is the most commonly diagnosed cancer in women worldwide, and also occurs in men. It is not a single disease but a group of conditions that differ substantially in how they behave and how they are treated, distinguished by the receptors the tumour cells carry. That distinction matters enormously: two women with tumours of identical size may receive entirely different treatment and face different outlooks depending on their tumour’s biology. Outcomes have improved markedly over recent decades through a combination of earlier detection, better understanding of these subtypes, and treatments targeted to them. Most women diagnosed today will not die of the disease, and the majority are treated without losing the breast.
What is it?
The breast consists of glandular tissue arranged in lobules that produce milk, ducts that carry it to the nipple, and supporting fat and connective tissue. Breast cancer arises when cells in this tissue acquire genetic changes allowing uncontrolled growth, most often beginning in the ducts and less often in the lobules.
The most important distinction is between non-invasive and invasive disease.
Ductal carcinoma in situ describes abnormal cells confined within the ducts, not having broken through into surrounding tissue. It cannot spread in this state, and is therefore not life-threatening as it stands. It is detected almost entirely through screening, since it rarely forms a lump, and it typically appears as a cluster of tiny calcium deposits on a mammogram. Its significance is that a proportion will progress to invasive cancer if left, and because it is not currently possible to identify reliably which ones will, it is generally treated. This creates a recognised tension: some women are treated for disease that would never have harmed them, and research into safely monitoring low-risk cases rather than treating all of them is ongoing.
Invasive cancer has broken through into surrounding tissue and can spread. Invasive ductal carcinoma, now often called invasive carcinoma of no special type, accounts for the large majority. Invasive lobular carcinoma is the next most common and behaves differently in a way that matters practically: it tends to grow in diffuse strands rather than forming a discrete lump, which makes it harder to feel and considerably harder to see on mammography, and it is more often diagnosed at a larger size or found only on MRI.
The feature that most determines treatment is not the type under the microscope but the receptors the cells carry, and understanding this transforms how the disease makes sense.
Hormone receptor-positive cancers carry receptors for oestrogen, progesterone, or both, meaning these hormones drive their growth. They account for roughly three-quarters of cases, generally grow more slowly, and are treated with endocrine therapy that blocks or removes that hormonal stimulation. Their outlook is generally favourable, though they retain a low but persistent risk of late recurrence extending many years after treatment.
HER2-positive cancers overproduce a protein that drives aggressive growth. Before targeted treatment existed these carried a notably poor outlook; the development of antibodies directed against HER2 changed this fundamentally, and it is one of the clearest examples of targeted therapy transforming a cancer’s prognosis.
Triple-negative cancers lack all three receptors, so neither endocrine therapy nor HER2-targeted treatment applies. They tend to occur in younger women, are more common in women of African ancestry and in BRCA1 carriers, grow faster, and have historically had fewer treatment options. Chemotherapy remains central, and immunotherapy has established an important role.
Several special types exist, including inflammatory breast cancer, which deserves specific mention because it does not present as a lump at all. It produces redness, swelling, warmth, and thickened skin with an orange-peel texture, developing over weeks. It is frequently mistaken for mastitis or infection and treated with antibiotics, and any breast inflammation that does not resolve promptly with antibiotics requires urgent specialist assessment. Paget disease of the nipple presents as persistent eczema-like change of the nipple and usually indicates underlying cancer.
The risk factors are well characterised, and understanding them helps place individual risk in context.
Being female and increasing age are the dominant factors, and nothing modifiable approaches them in magnitude.
Inherited gene alterations account for around 5 to 10 percent of cases. BRCA1 and BRCA2 are best known, carrying substantially elevated lifetime risks alongside ovarian cancer risk. PALB2 carries risk approaching that of BRCA2, and other genes including TP53, CHEK2, and ATM contribute. A family history of breast or ovarian cancer, particularly at young ages, in multiple relatives, or in men, warrants genetic assessment.
Reproductive and hormonal factors reflect lifetime oestrogen exposure. Early first period, late menopause, no pregnancies or first pregnancy after 30, and not breastfeeding all modestly increase risk, while pregnancy and breastfeeding reduce it. Combined hormone replacement therapy increases risk while taken, with the excess declining after stopping; oestrogen-only therapy carries less risk and is used in women without a uterus.
Breast density is an independent risk factor as well as a limitation of mammography. Dense tissue appears white on a mammogram, as do tumours, so cancers can be obscured—and separately, dense tissue carries a genuinely higher risk of cancer developing.
Lifestyle factors with established associations include alcohol, where risk rises with consumption in a dose-dependent way with no clearly safe threshold; obesity after menopause, since fat tissue becomes a source of oestrogen; and physical inactivity. Smoking is associated. Previous radiotherapy to the chest, particularly in adolescence or young adulthood for lymphoma, substantially increases risk and warrants specific surveillance.
Previous benign breast conditions including atypical hyperplasia and lobular carcinoma in situ raise risk and are markers rather than precursors in the usual sense.
Symptoms are varied, and the single most useful principle is that any new, persistent, unexplained breast change warrants assessment.
A lump is the most common presentation. It is characteristically firm, painless, and feels different from surrounding tissue. However, around one in six breast cancers presents with pain, so painful lumps should not be dismissed, and a painless lump is not reassuring.
Skin changes are important and include dimpling, puckering, tethering as the arm is raised, and the orange-peel texture associated with inflammatory disease.
Nipple changes include new inversion, a change in direction, persistent eczema-like scaling, and discharge—particularly when it comes from a single duct, occurs spontaneously without squeezing, and is bloodstained or clear.
Swelling in the armpit or above the collarbone reflects lymph node involvement and may occasionally be the first sign.
Most breast lumps are benign. Cysts, fibroadenomas, and normal nodularity account for the great majority, particularly in younger women. The purpose of assessment is to establish which is present, not to confirm an assumption either way.
Diagnosis follows triple assessment: clinical examination, imaging, and biopsy, with all three weighed together. Each can be misleading alone, and the combination is considerably more reliable than any component.
Mammography is the primary imaging test and the foundation of screening. It detects cancers before they can be felt, including the calcifications characteristic of ductal carcinoma in situ. Its principal limitation is dense breast tissue, where sensitivity falls appreciably. Digital breast tomosynthesis, which acquires images in slices, improves detection in dense tissue and reduces recall for false alarms, and is increasingly standard.
Ultrasound characterises lumps, distinguishes solid from cystic, assesses the lymph nodes in the armpit, and guides biopsy. It is the first-line imaging test in women under 40 and in pregnancy, where mammography is less informative and the breast tissue is typically dense.
MRI is the most sensitive test available. It is used for annual screening of women at high inherited risk, where it detects cancers mammography misses; for assessing the extent of disease before surgery in selected situations, particularly lobular cancer; and for monitoring response where chemotherapy is given before surgery. Its sensitivity comes at the cost of finding abnormalities that prove benign, so it is applied selectively rather than universally.
Core needle biopsy provides the diagnosis. Crucially, it also supplies the tissue for receptor testing—oestrogen, progesterone, and HER2 status—which determines treatment as much as the stage does. Where lymph nodes appear abnormal, they are sampled at the same time.
Genomic tests on the tumour, examining the activity of panels of genes, are used in hormone receptor-positive disease to estimate recurrence risk and identify which women genuinely benefit from chemotherapy. These have allowed a substantial number of women to safely avoid chemotherapy they would previously have received.
Screening deserves balanced description. Mammographic screening reduces deaths from breast cancer, and this is well established across multiple trials. It also carries recognised harms: false positives causing anxiety and additional procedures, and overdiagnosis—detecting disease, particularly ductal carcinoma in situ, that would never have caused harm. The balance is generally judged favourable in the age ranges where programmes operate, but it is a balance rather than an unqualified good, and women are entitled to understand both sides when deciding whether to attend.
Important to Know
The outlook for breast cancer has improved substantially, and this deserves stating clearly to anyone newly diagnosed. Most women diagnosed today will not die of the disease, survival at five years exceeds 85% in most high-income countries and is considerably higher for early-stage disease, and the majority are treated without losing the breast. Care is coordinated by a multidisciplinary team including breast surgeons, oncologists, radiologists, pathologists, specialist nurses, and genetics services.
Surgery is usually the first treatment, though chemotherapy or endocrine therapy is given first in some situations to shrink the tumour and allow less extensive surgery.
Breast-conserving surgery removes the tumour with a margin of surrounding tissue and preserves the breast. Combined with radiotherapy, it offers survival equivalent to mastectomy, and this equivalence is well established across long-term trials. Many women assume mastectomy must be safer; for most, it is not.
Mastectomy is appropriate for larger tumours relative to breast size, multiple tumours in different areas, where radiotherapy cannot be given, and where a woman prefers it. Reconstruction is available either at the same operation or later, and the options should be discussed before surgery rather than afterwards.
Sentinel lymph node biopsy identifies and removes only the first draining nodes, has replaced routine full axillary clearance, and has substantially reduced the incidence of lymphoedema—persistent arm swelling that was once a common and disabling consequence of treatment. Full clearance is now reserved for cases with significant nodal involvement, and even then its role has narrowed as evidence has accumulated.
Radiotherapy follows most breast-conserving surgery and reduces local recurrence. Modern schedules are considerably shorter than in the past, with evidence supporting courses of three weeks or fewer in many cases, and in selected older women with small hormone-sensitive tumours it may reasonably be omitted.
Endocrine therapy is the mainstay for hormone receptor-positive disease, given for five to ten years. Tamoxifen is used in premenopausal women and aromatase inhibitors in postmenopausal women, with ovarian suppression added for some younger women at higher risk. Adherence matters considerably—this treatment produces a substantial reduction in recurrence, but only if taken—and side effects including hot flushes, joint pain, and vaginal dryness are common and manageable. Women struggling with side effects should raise them rather than stopping, since alternatives and supportive measures exist.
HER2-targeted therapy, given alongside chemotherapy, has transformed outcomes in HER2-positive disease. Newer agents including antibody-drug conjugates have extended this further in both early and advanced disease.
Chemotherapy is used more selectively than it once was. Genomic testing in hormone receptor-positive, node-negative disease identifies women whose risk is low enough that chemotherapy adds little, and a substantial proportion can safely avoid it.
Immunotherapy is established in triple-negative disease, both before surgery in higher-risk early disease and in advanced disease, and has improved outcomes in a group with historically fewer options.
Advanced disease is treated with the aim of long-term control rather than cure, and this control can be prolonged. CDK4/6 inhibitors combined with endocrine therapy have substantially extended survival in hormone receptor-positive advanced disease. PARP inhibitors are effective in BRCA-related cancers. Many women live well for years with metastatic disease, and the framing of advanced breast cancer as a long-term condition is increasingly accurate.
Genetic testing is recommended for women diagnosed young, with triple-negative disease, with a significant family history, with male breast cancer in the family, or with Ashkenazi Jewish ancestry, and criteria have broadened. Identifying a mutation affects surgical choices, opens access to specific treatments, and has major implications for relatives, who can be tested and offered effective risk-reducing options.
Men with breast cancer deserve specific mention. It is uncommon but not rare, is frequently diagnosed later because neither men nor clinicians consider it, and presents as a lump beneath the nipple or nipple change. Any breast lump in a man warrants assessment. Treatment follows similar principles, with most male breast cancers being hormone receptor-positive.
Survivorship care matters and extends well beyond the end of active treatment. Long-term issues include menopausal symptoms, bone density loss with aromatase inhibitors, fertility concerns in younger women, lymphoedema, fatigue, cognitive effects, cardiac monitoring after certain treatments, sexual function, and fear of recurrence. These are legitimate concerns deserving active management rather than endurance.
Fertility preservation should be discussed before treatment with any woman who may want children, since chemotherapy can affect ovarian function and endocrine therapy requires years during which pregnancy is deferred.
Risk reduction is meaningful for women at high inherited risk, who may be offered enhanced surveillance with MRI, risk-reducing medication, or risk-reducing mastectomy, which substantially lowers risk. These decisions are highly individual and are made with specialist genetics input.
Care is coordinated by specialist breast units, and outcomes are better where care is delivered by experienced multidisciplinary teams. Imaging, pathology, receptor status, genomic findings, and clinical assessment are interpreted together alongside a woman’s age, health, and priorities.
Patient education plays an important role. Understanding that breast cancer is several different diseases with different treatments, that receptor status matters as much as stage, that breast-conserving surgery is as safe as mastectomy for most women, that chemotherapy is no longer given to everyone, that endocrine therapy only works if taken, and that most women diagnosed today survive their disease all contribute to appropriate care and informed decisions.
Red flag symptoms include any new breast lump or thickened area, in women or men; a lump in the armpit or above the collarbone; dimpling, puckering, or tethering of the skin; redness, swelling, warmth, or orange-peel skin texture, particularly if not resolving with antibiotics, which may indicate inflammatory breast cancer and requires urgent assessment; new nipple inversion or change in direction; persistent eczema-like change, scaling, or ulceration of the nipple; spontaneous discharge from a single duct, especially if bloodstained; a change in breast size or shape; persistent bone pain, breathlessness, or unexplained weight loss in someone previously treated; and any new symptom in a woman with a known high-risk gene alteration. These warrant prompt medical evaluation.