Why is cancer so common?

A chest X-ray showing cancer in the right lung A chest X-ray showing cancer in the right lung

Hundreds of thousands of people are diagnosed with cancer every year in the UK. It is not one disease; there are over 200 different types, each with its own symptoms, methods of diagnosis and treatment.

What is cancer?

Cancer starts when cells in our bodies start to reproduce out of control, forming new, abnormal cells. These abnormal cells form lumps, known as tumours.

If the cells from tumours cannot spread, then the tumours are benign. They are not cancerous and can usually be removed.

If the cells are able to invade nearby healthy tissue and organs, or spread around the body through the blood or lymphatic system causing further tumours to grow, then the tumours are malignant or cancerous. These cancer cells are likely to spread if the tumour is not treated.