They hope that eventually, doctors will be able to gauge an individual woman's risk of developing cancer by looking closely at her genetic makeup.

Only a small proportion of breast cancer cases are currently thought to be caused by inherited genetic factors.

Two genes have already been firmly linked with some cases of inherited breast cancer, but researchers are sure that there must be many more.

The team at Cambridge University's Department of Oncology now believes it has identified mutations in six other genes which have a link to breast cancer risk.

Although these are "tentative" early results, they will now carry out further experiments to strengthen their evidence.

While in diseases linked to a single mutated gene it is more straightforward to identify the gene involved, it is a highly complex task to work out the individual roles and importance of several genes which may be interacting to cause the disease.

Professor Bruce Ponder, who leads the team, told the ECCO cancer conference in Lisbon on Wednesday that gene screening may eventually prove more reliable than using other established risk factors as a guide.

Known risk factors include age, age of first period and menopause, high-fat diet, and high alcohol consumption.

Established risk factors are very important, but they are not good discriminants of risk for the individual

Professor Bruce Ponder, CRC Department of Oncology, Cambridge University

He said: "The number and type of genes that account for the remainder of familial breast cancer is not clear.

"It is, however, plausible, that at least some of this genetic predisposition is attributable to the effects of multiple, common, but individually weak genes."

'Genetic profile'

Every woman, he said, might be able to have her own "genetic profile" which would closely predict her risk of breast cancer.

He added: "Established risk factors are very important, but they are not good discriminants of risk for the individual.

"It's been shown that if you take a series of 10,000 women and evaluate them according to these factors, you can predict fairly accurately how many of them will get breast cancer.

"What you can't do is to tell which women will get it and which won't.

"We hope that the genetic profiles will be much more specific."