Up to 86,000 women in their thirties with a family history of breast cancer should receive annual mammograms, researchers say.
A new study funded by the charity Breast Cancer Now found cancers were picked up in younger age groups than those covered by current NHS screening, which often starts at age 40 for women known to be at risk.
The new study suggests that screening should be extended to women aged 35 to 39 with a family history - at a time when tumours may still be small and the cancer has not spread.
Breast Cancer Now’s chief executive Baroness Delyth Morgan said: “This could be an enormous breakthrough.
“We believe these findings could be practice-changing, and urge the Government’s upcoming review of NHS screening programmes to set out what further evidence is needed to consider screening for women aged 35 to 39 who are at increased familial risk of breast cancer.”
The research, carried out at 34 UK screening centres, found that annual mammograms for women aged 35 to 39 at moderate or high risk of breast cancer detected tumours when they were significantly smaller in size, compared with a group of women who were not screened.
Experts also found that earlier screening meant tumours were less likely to have spread to the lymph nodes - a sign that cancer is spreading around the body.
For the study, experts led by a team at the University of Manchester, writing in the journal EClinicalMedicine from The Lancet, examined data for 2,899 women from 2006 to 2015.
The women were all aged 35 to 39 and at moderate or high risk of breast cancer due to their family history, such as a mother or sister having the disease at a young age.
In total, 50 breast cancers were detected (in 49 women), of which 35 were invasive tumours.
Of the 35 tumours, 80% (28/35) were detected by screening when the tumour was 2cm or smaller in size, and only 20% (7/35) had spread to the lymph nodes.
The trial compared the results with a group of women aged 35 to 39 who were at increased risk but did not undergo screening.
In this group, far fewer cancers were detected when they were still small (45%) and far more of the women’s tumours had already spread to the lymph nodes.
Researchers said annual screening at age 35 to 39 could benefit between 64,000 and 86,000 women in the UK.
Current guidelines from the National Institute for Health and Care Excellence (Nice) recommend annual screening for women aged 40 to 49 who are at moderate or high risk of the disease.
Lead author Professor Gareth Evans, from the University of Manchester, said the results of the new trial were “very promising”.
He added: “Our trial shows that mammography screening is effective in detecting tumours earlier in this younger age group, and lays the groundwork for extending this screening in women at moderate or high risk down to women aged 35 to 39 from ages 40 to 49.
“Overdiagnosis is also far less likely to be a major issue in such a young age group.
“For women with a family history, removing a non-invasive tumour so early in their lives is likely to be a cancer preventive.”
Breast cancer is the leading cause of death in women under 50 in England and Wales - with more than 920 women dying from the disease in 2017.
Across all ages, breast cancer is the UK’s most common cancer, with around 55,000 women and 350 men diagnosed each year in the UK.
Experts believe that around 5% to 15% of breast cancers are linked to a family history of the disease.
Baroness Morgan said: “Early detection remains absolutely critical to stopping women dying from breast cancer.
“With breast cancer still the leading cause of death in women under 50, we need to find ways to identify those most at risk and offer them interventions earlier.
“We’ve long known that a family history can define a woman’s risk, and that breast cancer can be more aggressive in younger women.
“So, if we can intervene earlier for those at higher risk through annual screening, we believe we may be able to stop the disease cutting so many women’s lives so heartbreakingly short.”
Baroness Morgan said more research was now needed, including on the potential costs of extending screening.
An NHS England spokeswoman said an upcoming review by Professor Mike Richards will consider changes to the screening programme.
“Breast cancer survival is at its highest ever and with improved screening a key focus of the NHS long term plan, even more cancers will be diagnosed earlier,” she added.