Health reporter, BBC News
Annual screening for women in their 40s with a family history of breast cancer may save lives, research suggests.
The NHS breast screening programme currently offers mammograms to women aged between 50 and 70.
But UK researchers say a pilot study suggests regular mammograms should be given to younger women who have relatives with breast cancer.
A cancer charity said more data was needed to weigh up risks and benefits.
The study, published in the journal Lancet Oncology, looked at women deemed at moderate risk of breast cancer because they have relatives with the disease.
Screening is considered unjustified in women with no family history of breast cancer because of the risk of a false-alarm.
Women at high-risk - because they are thought to have a gene mutation associated with the disease - are already closely assessed, with many given MRI scans or offered early surgery.
The study recruited 6,710 moderate risk women across the UK who were given mammograms to check for signs of breast cancer every year for four years.
These women are not currently included in the main NHS breast screening programme, which offers mammograms to women aged 50-70 every three years.
The researchers, led by Professor Stephen Duffy of Barts and The London School of Medicine and Dentistry, Queen Mary, University of London, compared cancer rates and deaths in this group with women from other trials who were not given annual screening.
They say the women given screening were significantly more likely to be alive 10 years after a diagnosis of cancer than women in the two control groups.
Professor Duffy told the BBC: "It means that annual mammography does reduce the risk of dying of breast cancer in this group of moderate risk women.
"It means they can go and seek medical help knowing that there is something that can be done."
Rough figures suggest that it would probably save an extra 50 lives a year, he added.
"It doesn't sound like much but it means alot to the people who are in that group because they have relatives who have had breast cancer," he explained. "It's not a huge expense to the NHS."
But Hazel Nunn, senior health information manager at Cancer Research UK, said the full picture was not yet clear.
"Since it seems 5,000 women would need to be screened to save one life, it will be important to weigh up these benefits carefully against potential risks of routine mammography before deciding whether screening really is the best course of action for this group," she said.
"We await the results of further research measuring the risks."
The NHS Breast Screening Programme said plans were in place to extend screening to women with a family history of breast cancer in the future.
Assistant Director, Sarah Sellars, said current guidelines for women at risk of breast cancer because of their family history recommend that certain women should be offered surveillance.
She said these services were currently commissioned locally but in the future would be run by them.
"In the future, the NHS Breast Screening Programmes will be taking on responsibility for routinely screening higher risk women under 50," she said.
"Several breast screening sites are currently testing the software to be able to manage these women effectively.
"This service will sit alongside our current breast screening programme for women aged 50 years old and over."