Magnetic resonance imaging is more effective at detecting breast cancer in high risk women than traditional mammography, a study suggests.
A minority said they would rather not know if they had breast cancer
Researchers say use of MRI scans could reduce the need for precautionary breast removal operations.
They found the scans were almost twice as sensitive as X-ray mammography (XRM) in detecting cancer in women under 50 at high genetic risk.
The study, by the Institute of Cancer Research, is published in The Lancet.
Around 2% of breast cancer is due to the recently discovered breast cancer gene mutations BRCA1 and BRCA2.
Women with one of these gene mutations come from families where there is a strong family risk of breast cancer, and more than half of them will develop breast cancer by the age of 70.
Annual mammograms are offered to women with these gene mutations to allow early identification and treatment of tumours.
However, as women below the age of 50 often have dense breasts, mammography is not always very effective at detecting tumours.
As a result, around 40% of women at high risk opt to have their breasts removed rather than run the risk of developing cancer.
More accurate diagnosis of cancer would mean that treatment could start at an early stage, and surgery would require the removal of just the affected tissue, rather than the whole breast.
The latest study, which included 649 women, looked at whether MRI would be more helpful in detecting tumours within this group.
It found that MRI managed to identify 77% of tumours in women at high genetic risk - compared to just 40% using XRM.
Combining both XRM and MRI screening methods, enabled the detection of 94% of tumours.
MRI screening was particularly effective for women known to carry the BRCA1 gene mutation - detecting 92% of tumours, whereas XRM only detected 23%.
Lead researcher Professor Martin Leach said: "This study demonstrates that MRI screening is almost twice as sensitive as traditional X-ray mammography in identifying tumours in women of this age group at high genetic risk.
"As this study was carried out on a countrywide scale, the results represent a realistic assessment of how effective the method would be if it were implemented as a service."
Dr Ros Eeles, who also worked on the study, said: "We might finally now have an alternative to prophylactic mastectomy for women at high risk of breast cancer."
Dr Eeles accepted MRI scans were expensive, and not widely available. But she they would only be needed for around 1,000 women a year found to be carrying the dangerous gene mutations.
Liz Carroll, head of clinical services at the charity Breast Cancer Care, said the results were "interesting".
She said: "It may have implications for screening young women (below the age of 50) who are at high risk of developing breast cancer due to a genetic mutation.
"However, it is important to remember that mammograms are effective in screening the general population and women can continue to be confident in the national breast screening programme."
Antonia Bunnin, of the charity Breakthrough Breast Cancer, called for the National Institute for Health and Clinical Excellence (NICE) to review its guidance on the use of MRI for breast scans as soon as possible.
At present NICE recommends that high risk women have a mammography once a year.
It is currently considering fresh guidance on the appropriate use of MRI scans.