A treacherous chemical messenger which usually helps to fight infection may turn against the body and help to spread ovarian cancer, researchers have found.

The culprit, identified by a team lead by Professor Frances Balkwill, of Cancer Research UK, is a chemical from a group known as the chemokines called CXCL12.

It appears to increase the ability of ovarian cancer cells to move around the body - and may also help them to flourish once they reach other organs.

Chemokines usually play a highly valuable role in helping to fight infections by attracting healing cells - such as white blood cells from the bone marrow - to troubled areas.

But the new study suggests that sometimes they can have a highly damaging effect.

Wrong time and place

Professor Balkwill said: "If chemokines are made in the right place at the right time in the correct amount for the correct period of time then they are really very useful.

"But if they are made in the wrong place at the wrong time and for too long that's when they cause a problem."

The next stage is for scientists to find what will inhibit these unwanted actions of chemokines.

There is evidence that some drugs, currently used in the treatment of advanced cases of HIV/AIDS, do stop cells responding to the chemokine.

Sir Paul Nurse, chief executive of Cancer Research UK, said: "Each new discovery that tells us something about the way tumours behave and how they spread in the body is very important in adding to the bank of information that will ultimately enable us to control the progress of cancer."

Ovarian cancer is the fourth most common cancer among women in the UK. Each year, there are over 6,820 new cases.

The risk of ovarian cancer increases with age. Most ovarian cancers occur in women after they have gone through the menopause. Half of all ovarian cancers occur in women over the age of 65.

Other studies have identified different chemokines in a variety of other cancers, including breast cancer.

The study is published in the journal Cancer Research.