The researchers from The University of Manchester -- part of Manchester Cancer Research Centre -- looked at 691 women who had undergone genetic testing and were confirmed as carrying a mutation in either the BRCA1 or BRCA2 gene before they had developed cancer. The study, funded by Genesis Breast Cancer Prevention, the UK's only charity entirely dedicated to the prediction and prevention of breast cancer. The results were published recently in Breast Cancer Research and Treatment.

Just over one-third of women in this study opted for preventative surgery. The researchers compared outcomes for those who chose to have risk-reducing surgery with those who did not.

Professor Gareth Evans, from The University of Manchester -- part of Manchester Cancer Research Centre, said: "The research shows a major benefit from undergoing risk-reducing surgery, particularly removal of the ovaries and fallopian tubes which reduces the risk of both ovarian cancer greatly and breast cancer by about half."

The Manchester researchers found that women who had any form of risk-reducing surgery had increased survival compared to those deciding against such an operation. Life expectancy was almost normalised in those that underwent surgery but substantially reduced in those who did not.

Further research is now needed to assess the possible advantage of a double mastectomy alone.

Professor Evans, who is a Consultant in Clinical Genetics at Central Manchester NHS Foundation Trust and part of the Manchester Centre for Genomic Medicine, added: "In the past some women have thought that MRI screening is so good that they don't need to have removal surgery but our research has shown despite intensive screening quite a few of these women, particularly with the more aggressive BRCA1 gene, were dying and perhaps being lulled into a false sense of security by screening.

"Following Angelina's announcement there has been a three-fold increase in the number of women with a family history of breast and ovarian cancer coming forward asking about surgery. It really has raised the public awareness of this.

"Decisions particularly to have breast surgery take a long time. Many people weigh it up in the balance for a number of years and a catalyst might be if there's another death in the family. There is no doubt that the most effective method for a woman at risk is to have her ovaries removed and we are pretty close to certain that removing breast tissue increases life expectancy but more research is needed.

"Ideally all women who are at risk should be tested and followed for life to assess the true impact of risk-reducing surgery. However, many women do not wish to know their gene status and longer term follow up of those who do opt for testing while still unaffected with cancer is required to assess the true overall benefit."