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Around 7,600 women in their 40s are diagnosed with breast cancer every year in the UK. But the NHS Breast Screening Programme only starts inviting women once they turn 50. Mammography (X-ray of the breasts) is offered to women every three years between the ages of 50 to 70.

There is long-standing debate about the possible benefits and harms of screening younger women. While it might reduce deaths from breast cancer, it might also find cancers that would never have caused the woman harm (over-diagnosis). This causes distress and means that she undergoes treatment – drugs, surgery and/or radiotherapy – of no benefit to her.

A long-term trial began in the 1990s to look at the impact of offering annual mammography to women in their 40s. It found that screening these younger women prevented breast cancer deaths in the first ten years but not afterwards. It did not increase over-diagnosis compared to the current programme. This suggests that women in their 40s might benefit from annual screening.

Other NHS screening programmes are competing for a limited budget. The cost-effectiveness of a policy change to include younger women needs to be explored.

What’s the issue?

Around 55,000 women are diagnosed with breast cancer every year in the UK. Most of these women are 50 or over, but about 10,000 women under the age of 50 are diagnosed every year. Around 7,600 of these women are in their 40s.

The NHS Breast Screening Programme offers regular mammography screening to women aged 50–70. It has been proven to reduce deaths from breast cancer.

A change of policy to include women in their 40s is controversial. It might reduce deaths from breast cancer, but some experts doubt this. There is evidence that screening is less effective in younger women possibly because they have more dense breast tissue than older women, which makes it difficult for tiny cancers to be spotted on X-rays. Some experts have concerns about over-diagnosis, when women with cancers that would not have caused harm, suffer unnecessary distress and treatment.

This research concludes a long-term trial that offered annual mammography to women in their 40s.

What’s new?

During the 90s, the study recruited 160,836 women aged 39-41. Around one-third of these women were randomly selected to be screened for breast cancer in their 40s. They received invitations for annual mammography screening until the year of their 48th birthday. The remaining two-thirds of women were the comparison group and were not invited for screening in their 40s.

At the age of 50, both groups of women became eligible for screening every three years as part of the existing NHS Breast Screening Programme.

The researchers followed up all the women for an average of 23 years. They recorded breast cancer diagnoses, deaths from breast cancer and deaths from any other causes.

The trial found that annual screening of women in their 40s prevented one death for every 1000 women screened. Compared to those receiving standard screening (starting at age 50), these women:

  • were 25% less likely to die of breast cancer in the first 10 years of the trial
  • had a similar reduction in risk of death beyond 10 years
  • had no increased risk of deaths from other causes.

The trial found some overdiagnosis of women screened in their 40s. But overall, this group had no extra risk of over-diagnosis beyond that expected among women over 50 in the NHS Breast Screening Programme.

Why is this important?

The results suggest that women in their 40s may benefit from annual screening for breast cancer. Screening in this way prevented approximately one death for 1,000 women screened.

After 10 years, the effect of this early screening on deaths was reduced. This may be because screening in younger women is less able to identify aggressive (grade 3) tumours at an early stage. These tumours grow and spread more quickly than other (lower grade) tumours and are more likely to be fatal. Further research is needed to confirm this.

The study found no greater risk of over-diagnosis when screening started at a younger age. This suggests that extending the screening programme would not increase its harms.

What’s next?

This research screened women using film mammography. It took two-views at the first screen only, and single-view after. Now, screening is digital with two views at every screening. These changes, coupled with improved resources and higher compliance with screening, might mean that more breast cancer deaths could be prevented in women in their 40s.

Treatment for breast cancer has improved since the study began. In combination with earlier screening, these therapies could lead to an even greater reduction in deaths than that found in this research.

It is important to note that other NHS screening programmes are competing for a limited budget. The cost-effectiveness of a policy to screen women for breast cancer in their 40s needs to be explored and weighed up against the value of other interventions.

You may be interested to read

The full paper: Duffy SW, and others. Annual mammographic screening to reduce breast cancer mortality in women from age 40 years: long-term follow-up of the UK Age RCT. Health Technol Assess. 2020;24

Related research paper: Smith RA, and Oeffinger KC. The Importance of Cancer Screening. Med Clin North Am. 2020;104:919-938

Related research paper: Zielonke N, and others. The potential of breast cancer screening in Europe. Int J Cancer. 2021;148:406-418


Funding: This project was funded by the NIHR Health Technology Assessment programme.

Conflicts of Interest: The study authors declare no conflicts of interest.

Disclaimer: NIHR Alerts are not a substitute for professional medical advice. They provide information about research which is funded or supported by the NIHR. Please note that views expressed in NIHR Alerts are those of the author(s) and reviewer(s) and not necessarily those of the NHS, the NIHR or the Department of Health and Social Care.

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