Women with a family history of breast cancer should be offered a hi-tech scan to check for disease, experts say.
The round orange circle in this MRI image is a tumour
The National Institute for Health and Clinical Excellence says these women, when aged 20 to 49, should have yearly magnetic resonance imaging (MRI) scans.
An MRI scan costs about £350, 10 times the cost of a mammogram.
Breast cancer groups welcomed the NICE guidelines and said they provided the "safety net" that women at high risk of the disease wanted.
Any woman considered to have a high risk of breast cancer, including those who carry one of the faulty high-risk genes, such as BRCA1 or BRCA2 will be eligible for the scans.
The guidance for doctors sets out when women should be given MRIs.
For women aged 20 to 29, it says MRI scans "should be available only for those at exceptionally high risk (that is, annual risk greater or equal to 1%)."
For those aged 30 to 39, those at high risk of carrying faulty genes such as BRCA1 or TP53, or those with a 10-year risk that is greater than 8% should be checked.
And in the 40 to 49 age-group, MRI scans should be offered to those with a 10-year risk greater than 20%, as well as women with a 10-year risk greater than 12% whose mammography "has shown a dense breast pattern".
NICE published initial guidance on checks for women in this group two years ago, before the data on MRI scanning was available.
'A vital new option'
NICE chief executive Andrew Dillon said: "The studies show greater sensitivity of MRI in detecting breast cancer at an early stage in women who are at high risk of developing breast cancer due to their family history, and we have therefore recommended its use this group."
Breakthrough Breast Cancer chief executive Jeremy Hughes said: "MRI screening is a vital, new option for younger women who have a genetic risk of breast cancer.
"It's also important that existing government commitments are met.
"Unfortunately, many women are still facing unacceptable delays to find out if they have faulty BRCA genes, which puts them at a lifetime risk of developing breast cancer of up to 85%.
"Anyone who takes a genetic test must be guaranteed the highest quality test and receive their results within two or eight weeks, as recommended by the government."
Anna Wood, of Breast Cancer Care said: "The challenge now is to ensure that the NHS has adequate resources to allow it to implement this guidance, and be able to offer MRI screening to these patients throughout England and Wales."
Hereditary Breast Cancer Helpline director Wendy Watson said: "Anything that offers more options to women at increased risk has to be a clear advantage."