What is Breast Cancer?

What is breast cancer?

Breast cancer is a disease in which cells in the breast grow uncontrollably and form a tumour. The breast is made up of three main parts: lobules (glands that produce milk), ducts (tubes that carry milk to the nipple) and connective tissue. Most breast cancers begin in the ducts or lobules.

Breast cancer is the most commonly diagnosed cancer in women worldwide, with around 2.3 million new cases diagnosed each year according to the World Health Organization. In the UK, around 56,000 people are diagnosed with breast cancer annually — the vast majority of them women, though around 400 men are also diagnosed each year.

How does breast cancer develop?

Cancer begins when the DNA inside normal breast cells mutates or changes, causing the cells to grow and divide faster than they should and to continue living when healthy cells would normally die. These abnormal cells accumulate and form a mass of tissue — a tumour. Some breast tumours are benign (not cancerous) and do not spread. Others are malignant (cancerous) and can grow into nearby tissue or spread to other parts of the body.

Breast cancer can spread when cancer cells travel through the lymphatic system or the bloodstream to other parts of the body — most commonly the bones, liver, lungs and brain. This is called secondary or metastatic breast cancer.

Who is at risk?

Any woman can develop breast cancer. The biggest risk factor is simply being female and getting older — most cases are diagnosed in women over 50. Other risk factors include a family history of breast cancer, inherited gene mutations (especially BRCA1 and BRCA2), having had previous breast cancer, dense breast tissue, and certain lifestyle factors such as alcohol consumption, being overweight after the menopause, and not having children.

However, the majority of women who develop breast cancer have no obvious risk factors beyond age and sex. This is why general screening — not just high-risk monitoring — matters.

Why early detection matters

The stage at which breast cancer is detected is the single biggest predictor of survival. When breast cancer is found at Stage 1 (small, localised tumour), the NHS five-year survival rate is around 98%. By Stage 4, when the cancer has spread to distant organs, that figure falls to around 26%.

In the UK, widespread NHS mammography screening and good public awareness mean that many cancers are caught early. In low-income countries, the absence of screening programmes and poor health literacy mean that most cases are found at an advanced stage — which is why survival rates in countries such as Pakistan and Indonesia are far lower than in the UK.

Common myths — and the truth

• Myth: "A lump that doesn't hurt can't be cancer." Truth: Most early breast cancer lumps are painless.
• Myth: "Cancer is caused by a blow or bruise." Truth: Injuries do not cause cancer — they may draw attention to a pre-existing lump.
• Myth: "If no one in my family has had it, I won't get it." Truth: Most women who develop breast cancer have no family history of the disease.
• Myth: "Deodorant or underwired bras cause breast cancer." Truth: There is no scientific evidence for either claim.