Many people ask themselves why cancer has happened to them or to a close relative. People often feel that cancer is such an awful disease that they want to know why they developed it. They might think about their own medical history or about risks in the environment. People sometimes also think that several cases of cancer in their family might be connected, and that they have inherited an increased risk of developing cancer. However, only a minority of cancers (5–10%, or less than 10 out of 100 cases) are clearly linked to an inherited gene change. Unfortunately, most cancers happen for reasons we don't fully understand.

Cancer is a common disease. It is estimated that in the UK about 1 in 3 people will get cancer during their lives. Most people who get cancer are over 65. It is relatively rare for young people (people under 50) to get cancer. If you have only one elderly relative with cancer, you are not usually at a significantly increased risk of getting the same cancer yourself.