Breast cancer is a disease in which abnormal cells in the breast grow out of control and form a tumour. These cancer cells usually start in the milk ducts or the milk-producing lobules of the breast; if left untreated, they can invade nearby tissue and spread (metastasize) to other parts of the body.

How breast cancer develop

Breast tissue contains ducts (which carry milk to the nipple) and lobules (which make the milk). Most breast cancers begin in the cells lining these ducts (ductal) or in the lobules (lobular). Some early changes, such as ductal carcinoma in situ (DCIS) or lobular carcinoma in situ (LCIS), are non-invasive or are considered high-risk changes rather than invasive cancer. If malignant cells break out of the ducts or lobules into surrounding tissue, the cancer is called invasive.

Common types of breast cancer

• Ductal carcinoma in situ (DCIS) — non-invasive (stage 0) cancer cells are inside a duct.
• Invasive ductal carcinoma (IDC) — cancer that began in a duct and has invaded surrounding tissue (the most common invasive type).
• Invasive lobular carcinoma (ILC) — begins in lobules and can spread into nearby tissue.
• Less common/other types — inflammatory breast cancer, HER2-positive cancers, triple-negative breast cancer, and others; each has different behaviour and treatment approaches.

Symptoms to watch for

Early breast cancer often has no symptoms, which is why screening matters. When symptoms occur they may include:

• A new lump or thickening in the breast or underarm.
• Change in breast size, shape or appearance.
• Dimpling of the skin, nipple retraction, or scaly skin on the nipple.
• Nipple discharge (not breast milk) or unexplained breast pain.
• If you notice any persistent change in your breasts, get evaluated by a healthcare professional.

What increases the risk?

Risk is influenced by a mix of non-modifiable and modifiable factors:

• Non-modifiable: being female, increasing age, family history of breast cancer or inherited gene changes (BRCA1/BRCA2), certain benign breast conditions.
• Modifiable/other influences: obesity after menopause, alcohol consumption, certain hormone therapies, and reproductive history (e.g., age at first childbirth). Risk factors raise probability but don’t guarantee disease.

How breast cancer is diagnosed

Diagnosis typically includes a combination of:

• Clinical exam (by a clinician).
• Imaging — mammography is the standard screening tool; ultrasound and MRI may be used for further evaluation.
• Biopsy — sampling tissue or cells to confirm cancer and determine the type, grade, and biomarkers (e.g., hormone receptors, HER2).

These tests together guide staging and treatment planning.

Treatment options (tailored to the person and the cancer)

Treatment depends on the type, stage, and tumour biology and may include:

• Surgery (lumpectomy/mastectomy) to remove the tumour.
• Radiation therapy to destroy remaining cancer cells after surgery.
• Systemic therapies: chemotherapy, hormone (endocrine) therapy, targeted therapy (e.g., for HER2-positive cancers), and immunotherapy in selected cases.

Multidisciplinary teams create personalized plans; many people receive a combination of treatments.

Screening and prevention

• Screening: Routine mammograms are recommended by health authorities for people in certain age groups/risk categories because they can detect cancers before symptoms arise. Screening recommendations differ by country and individual risk — talk to your clinician about what’s right for you.
• Prevention: Lifestyle changes (maintaining healthy weight, limiting alcohol, regular physical activity) may lower risk. People with very high inherited risk may consider enhanced surveillance or preventive options; genetic counselling is important where family history suggests inherited risk.