Breast cancer

Breast cancer is a malignant disease that arises from the cells of breast tissue, most commonly from the epithelial lining of the milk ducts or the lobules that produce milk. It is one of the most extensively studied cancers owing to its high global prevalence and the significant public health challenges it presents. Although it affects women far more frequently than men, breast cancer can occur in both sexes and across all age groups, with incidence strongly influenced by genetic, hormonal, environmental and lifestyle factors.
Breast cancer may remain asymptomatic for long periods and is frequently detected through routine screening programmes. When symptoms do occur, they often involve noticeable changes in the breast’s appearance or texture. Advances in diagnostic imaging, pathology, hormonal and targeted therapies, and surgical techniques have improved overall outcomes, although survival still varies markedly between countries depending on access to healthcare.

Signs, Symptoms and Clinical Features

While many individuals with breast cancer experience no symptoms at diagnosis, routine screening may reveal early-stage tumours. When symptoms are present, the most common is a new lump in the breast, though most lumps are benign. Features more suggestive of malignancy include lumps that are painless, hard, and irregular in shape. Additional symptoms may include:

• Alteration in breast shape or size.
• Dimpling or thickening of the breast skin.
• Redness, dryness or scaly skin over the breast or nipple.
• Nipple inversion or abnormal nipple discharge.
• Swelling of lymph nodes in the armpit or near the collarbone.

Less common forms of breast cancer present with distinctive signs. Inflammatory breast cancer, accounting for up to 5 per cent of cases, involves cancer cells obstructing lymph vessels, causing rapid swelling and redness of the breast. Paget’s disease of the breast, observed in a small proportion of cases, produces an eczemalike rash around the nipple and areola.
Advanced or metastatic breast cancer spreads most frequently to the bones, liver, lungs and brain. Symptoms of metastasis vary by site: bone metastases may cause progressive pain or fracture; liver involvement may lead to abdominal discomfort or jaundice; lung metastases may result in persistent cough or breathlessness; and brain metastases may provoke headaches, seizures or cognitive changes.

Risk Factors

A range of biological, lifestyle and hereditary factors influence breast cancer risk. Well-established factors include:

• Obesity and a sedentary lifestyle.
• Alcohol consumption and prolonged hormone replacement therapy in menopause.
• Exposure to ionising radiation.
• Early menarche, late first pregnancy, or having no children.
• Older age and a prior history of breast cancer.
• Family history of the disease.

Between 5 and 10 per cent of all cases arise from inherited genetic predisposition. Mutations in genes such as BRCA1 and BRCA2 significantly increase the lifetime risk of developing breast cancer.
Epidemiologically, breast cancer occurs more frequently in developed nations. For transgender individuals receiving gender-affirming hormone therapy, risk levels differ depending on the type of transition and duration of hormone exposure.

Screening and Early Detection

Breast cancer screening aims to identify tumours before symptoms emerge, improving treatment success and survival. Mammography, a low-dose X-ray technique, is the primary method and can detect tumours by identifying unusual densities, distortions in breast architecture or microcalcifications. Radiologists interpret mammograms using the BI-RADS classification system, which standardises reporting and helps assess the probability of malignancy.
Breast density influences mammographic sensitivity: fatty breasts allow detection of about 90 per cent of tumours, while extremely dense breasts may reduce detection to around 60 per cent. In such cases, adjunctive imaging—ultrasound, MRI, or tomosynthesis—can improve diagnostic accuracy.
Most medical guidelines recommend regular mammography for women aged 50–70, typically every one to two years. Screening may also reduce mortality in women aged 40–49, though recommendations vary by country. For women at high genetic risk, combined mammography and MRI is often advised.
Self-examination of the breasts has not been shown to lower mortality, and the benefits of clinician-performed breast examination remain uncertain. Screening in lower-income regions is less common due to limited access to imaging technology.
Despite its benefits, mammography may yield false positives or false negatives, causing anxiety or unnecessary procedures.

Diagnosis

If a suspicious finding is identified through screening or clinical examination, further imaging—such as diagnostic mammography or ultrasound—is used to clarify the nature of the abnormality. Definitive diagnosis requires a breast biopsy, typically performed via core needle biopsy using a hollow needle to remove tissue. Fluid-filled masses may be assessed by fine-needle aspiration.
Only around 10–20 per cent of biopsied lesions prove cancerous; many represent benign conditions such as fibrocystic changes. Once cancer is confirmed, staging investigations determine whether it has spread and guide therapeutic planning.

Classification and Types

Breast cancer encompasses several histological and molecular subtypes. The most common include:

• Invasive ductal carcinoma, originating from the ducts.
• Invasive lobular carcinoma, arising from milk-producing lobules.
• Ductal carcinoma in situ (DCIS), a non-invasive precursor lesion.

More than 18 additional subtypes are recognised, some defined by their cellular appearance and others by molecular markers. These distinctions influence treatment decisions and prognosis.

Treatment Approaches

Management depends on tumour type, stage and individual patient factors. Treatment options include:

• Surgery, ranging from breast-conserving operations to mastectomy.
• Radiation therapy, often used after breast-conserving surgery.
• Chemotherapy, administered pre- or postoperatively or for advanced disease.
• Hormonal therapies such as tamoxifen or aromatase inhibitors for hormone-sensitive cancers.
• Targeted therapies, including agents affecting HER2-positive tumours.

Breast reconstruction may be performed at the time of mastectomy or in a separate procedure. For metastatic disease, treatment aims primarily to improve quality of life and alleviate symptoms.
Preventive strategies include tamoxifen, raloxifene or preventive mastectomy in individuals with high genetic risk.

Prognosis and Global Epidemiology

Survival varies according to stage at diagnosis, tumour biology and healthcare access. Five-year survival rates in countries such as the United Kingdom and the United States range from 80 to 90 per cent, while lower-income countries report significantly lower outcomes due to later diagnosis and reduced treatment availability.
Breast cancer is the most common malignancy in women worldwide, accounting for roughly a quarter of all female cancer diagnoses. In 2018 it resulted in approximately two million new cases and over 600,000 deaths. Although predominantly a disease of women, it is more than one hundred times less common in men.