Why is cancer so common?

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.

More than one in three people will develop some form of cancer during their lifetime. In 2010 324,579 people in the UK were diagnosed with cancer (excluding non-melanoma skin cancer).

Every cell in our body contains DNA. It carries our genetic code and contains the instructions for all the cell's actions.

If the DNA inside cells is damaged, these instructions go wrong. In fact damage to the DNA or "mutations" as they are known, constantly occur in our cells as they divide and reproduce. Most of the time, the cells recognise that a mutation has occurred and repair the DNA, or self-destruct and die.

When a number of mutations have occurred in the DNA of a cell, control of cell growth may be lost and the cells do not die. Instead they start to follow abnormal instructions that make them reproduce and grow, producing more and more of these mutated cells - this is the start of a cancer.

Many factors such as smoking or too much exposure to the sun can also trigger DNA damage - leading to a faster accumulation of the mutations which lead to cancer.

A family history of cancer can also increase chances of getting the disease, because it usually means that person starts their life already having inherited some of the DNA mutations that take them down the path to cancer.

Even when in remission, those who have had the disease have a higher risk of it developing again. In most cases however, the exact cause or sequence of events by which cancer develops, is not yet known

A recent study has found that there are more than 80 genetic markers (i.e. mutated genes) that can increase the risk of developing breast, prostate or ovarian cancer, for example. Scientists believe the results could soon lead to widespread use of DNA profiling for these cancers, though individual genetic testing for those likely to be at increased risk such as when there is a strong family history of a type of cancer is already in use.

bbc.co.uk