Breast cancer

What it is

Breast cancer is a cancer that starts in breast tissue; about 2.4 million women were diagnosed worldwide in 2024. It develops when abnormal cells in the ducts or lobules of the breast grow out of control and form a tumour. The single most important practical fact is that breast cancer is often highly treatable when found early, before it has spread to lymph nodes or distant organs.

Breast cancer is the most common cancer in women globally, although it can also occur in men. WHO notes that about 0.5% to 1% of breast cancers occur in men, and around 80% occur in women without a specific risk factor other than sex and age. In India, breast cancer is a major public health problem and is one of the most commonly diagnosed cancers among women, especially in urban areas.

Breast cancers are commonly described by where they start and by their biology:

Type / feature	What it means
Ductal carcinoma	Starts in the milk ducts; this is the most common type
Lobular carcinoma	Starts in the milk-producing lobules
In situ cancer	Abnormal cells remain confined, such as ductal carcinoma in situ (DCIS)
Invasive cancer	Cancer has spread into surrounding breast tissue
Hormone receptor-positive	Cancer cells use oestrogen and/or progesterone signals to grow
HER2-positive	Cancer cells make too much HER2 protein
Triple-negative	Lacks oestrogen receptor, progesterone receptor, and HER2

These features matter because they guide treatment and help estimate prognosis.

How it works

Breast cancer begins when genetic changes allow breast cells to divide when they should not. Over time, these cells can invade nearby tissue, enter lymphatic channels or blood vessels, and spread to lymph nodes, bone, liver, lungs, or brain.

Several biological pathways are important:

1. Hormone signalling: Some breast cancers depend on oestrogen or progesterone. These cancers may respond to endocrine therapy.
2. HER2 signalling: HER2-positive cancers have overexpression or amplification of the HER2 gene, which can drive faster growth but may respond well to HER2-targeted drugs.
3. DNA repair defects: Inherited mutations such as BRCA1, BRCA2, and PALB2 can increase risk because cells are less able to repair DNA damage.

Risk rises with age, and other factors can contribute, including obesity, alcohol use, prior chest radiation, some reproductive factors, and postmenopausal hormone therapy. A family history increases risk, but most people diagnosed do not have a strong family history.

Diagnosis / how it's measured

Breast cancer is diagnosed by combining clinical examination, imaging, and tissue testing. A lump does not automatically mean cancer, but any persistent new breast change should be assessed.

Common steps include:

1. Clinical breast exam: A clinician checks for a lump, skin change, nipple change, or enlarged lymph nodes.
2. Imaging: Mammography is the main imaging test for many adults. Ultrasound is often useful, especially in younger women or to assess a specific lump. MRI may be used in selected high-risk or complex cases.
3. Biopsy: A core needle biopsy is usually needed to confirm the diagnosis. This is the key test because imaging alone cannot reliably define the exact cancer type.
4. Pathology and biomarkers: The biopsy is tested for histologic type, grade, oestrogen receptor (ER), progesterone receptor (PR), and HER2 status. These results strongly influence treatment.
5. Staging: Doctors determine tumour size, lymph node involvement, and whether there is distant spread. This is often summarised using the TNM staging system.

Symptoms that can lead to testing include a new breast lump, thickening, nipple discharge, nipple inversion, skin dimpling, redness, swelling, or a lump in the armpit. Some breast cancers are found on screening before symptoms appear.

Evidence and uses

Treatment depends on stage, tumour biology, age, menopause status, overall health, and patient preference. Most treatment plans use more than one approach.

Treatment	Main role
Surgery	Removes the tumour; may be breast-conserving surgery or mastectomy
Radiation therapy	Lowers local recurrence risk, often after breast-conserving surgery
Endocrine therapy	Used for ER- or PR-positive cancers
Chemotherapy	Used when recurrence risk is higher or disease is aggressive
HER2-targeted therapy	Used for HER2-positive cancers
Immunotherapy	Used in selected cases, especially some triple-negative cancers

Early-stage breast cancer is often treated with surgery followed by radiation, medicines, or both. Breast-conserving surgery plus radiation can offer survival outcomes similar to mastectomy for many patients with early disease. Systemic treatment may be given before surgery (neoadjuvant) to shrink the tumour or after surgery (adjuvant) to reduce recurrence risk.

For metastatic breast cancer, treatment usually aims to control the disease, relieve symptoms, and prolong life rather than cure it. Many people live for years with metastatic breast cancer because treatment options have expanded.

Supportive care also matters. This can include pain control, management of treatment side effects, physiotherapy for arm stiffness or lymphoedema, fertility counselling, psychosocial support, and palliative care when needed.

When to see a clinician

See a clinician promptly if you notice a new breast lump, persistent focal pain, nipple discharge that is bloody or spontaneous, skin dimpling, nipple inversion, breast swelling, or a lump in the armpit. Do not wait to see if a suspicious change disappears on its own.

Urgent review is also important if you have unexplained weight loss, bone pain, breathlessness, severe fatigue, or neurological symptoms after a breast cancer diagnosis, because these can sometimes suggest spread or treatment complications.

People with a strong family history of breast, ovarian, pancreatic, or prostate cancer may benefit from genetic counselling. This is especially relevant if cancers occurred at a young age or if there are multiple affected relatives.

Limitations and open questions

Breast cancer is not one disease. Outcomes vary widely by stage, tumour subtype, access to treatment, and overall health. Even within the same subtype, cancers can behave differently.

Screening and treatment continue to improve, but there are still open questions about the best way to tailor therapy, avoid overtreatment in low-risk disease, and overcome drug resistance in advanced cancer. Evidence is also evolving on how to use genomic tests, immunotherapy, and newer targeted drugs in different settings.

In India and other low- and middle-income settings, delays in diagnosis and unequal access to pathology, imaging, radiation, and targeted medicines can affect outcomes. If you are being evaluated for breast cancer, ask for the exact pathology type, stage, ER/PR status, and HER2 status, because these details are central to treatment decisions.