Wednesday January 9 2008
Mammogram screening can identify breast cancer early
Screening for breast cancer using mammography, halves the risk of death from breast cancer, according to The Guardian. Women “screened for breast cancer were 48% less likely to die of the disease than women who were not examined”, the newspaper said.
BBC News quotes a specialist from Cancer Research UK who says that “this is the strongest evidence yet that screening programmes like this save lives”. All women aged 50–70 are currently offered breast cancer screening in the UK, with a plan to extend the programme to those aged 47–73 in 2012.
The newspaper reports are based on research that has compared the screening histories of 300 women who died from the disease with 600 women of the same age, and has shown that NHS screening may be even more effective than previously estimated by the Advisory Committee on Breast Cancer. The benefits of breast cancer screening such as the earlier detection of the disease thus allowing treatment to begin sooner, are well known, and this study helps to quantify this.
Where did the story come from?
This research was carried out by Dr Prue Allgood and colleagues from Cancer Research UK, and the Department of Radiology, Addenbrooke’s Hospital and Strangeways Research Laboratory, both in Cambridge. It was published in the (peer-reviewed): British Journal of Cancer.
What kind of scientific study was this?
This was a case-control study designed to investigate the effect of breast cancer mammography screening on deaths from the disease in East Anglia, and to see whether the size of the effect is similar to that seen in randomised controlled trials.
NHS breast cancer screening was established in East Anglia in 1989, and since then all women aged 50–70 have been invited to attend for mammography every three years. The researchers used the East Anglia Cancer Registry Database to randomly identify 300 women in this age group who had been diagnosed with breast cancer after 1995, and who had died from the disease. All “cases” had to have been invited for screening at least once before they were diagnosed.
The researchers matched each “case” with two "controls" – women of the same age who were still alive, identified through the NHS Exeter system database and individual screening units. They compared breast cancer screening between the two sets of women, including the number of invitations for screening, the number of screening visits, and the outcomes of the screening. They adjusted for the main factor known to influence screening attendance – socioeconomic status.
What were the results of the study?
The average age of breast cancer diagnosis was 60.7, and the average age at first screening was 55. The researchers found that the women in the “case” group attended significantly fewer screening sessions (1.4 attendances for cases compared with 1.7 for controls). They also found that the risk of death from breast cancer was reduced by 48% in woman who were invited for and received screening. This figure took into account the fact that healthier women may be over-represented in screened populations. They found a general trend towards an increase in risk of death with number of years since last screened. There was no link between death from breast cancer and the number of screening sessions attended.
What interpretations did the researchers draw from these results?
The authors conclude that their results show that receiving breast cancer screening reduces the number of deaths from the disease in East Anglia. They say that these results are consistent with evidence found from randomised controlled trials.
What does the NHS Knowledge Service make of this study?
The benefits of breast cancer screening in aiding earlier detection of the disease, therefore allowing treatment to start more quickly, are well recognised, and this study helps to show some of the size of this benefit. A few points to bear in mind when reading this research, which the authors acknowledge:
- As they have only considered cases diagnosed after 1995, the cases of breast cancer are likely to be more advanced for deaths to have occurred in the relatively short space of time of their follow-up period. This may not be representative of all breast cancer .
- These results were only obtained from the East Anglia region, and may not necessarily be the same as elsewhere in the UK. The authors recommend research in other regions and countries.
- The research has examined the benefits of screening in terms of earlier detection and thereby reducing risk of death through earlier treatment. Other factors such as age at diagnosis, and stage and size of tumour may all ultimately have an effect upon the treatment options available and prognosis.
- Women who take up the invitation to attend screening may be healthier than those who decide not to attend. The researchers controlled for this possible bias by adjusting for socioeconomic status. It is unclear whether this is an appropriate way to adjust for this potential problem with the sample.
Sir Muir Gray adds...
I am hopelessly biased in assessing this report because I was responsible for setting up the screening programme, but I do find this report very encouraging.
Links to the headlines
Screening halves breast cancer deaths says study. The Guardian, January 9 2008
Death rate falls due to screening. Daily Mirror, January 9 2008
Breast cancer screening 'halves risk of death'. The Daily Telegraph, January 9 2008
Breast screening 'really works'. BBC News, January 9 2008
How NHS screening beats breast cancer. Daily Express, January 9 2008
Screening has halved breast cancer deaths. Metro, January 9 2008
Links to the science
Allgood PC, Warwick J, Warren RML, et al. A case-control study of the impact of the East Anglian breast screening programme on breast cancer mortality. Br J Cancer 2008; 98:206–209.
Gøtzsche PC, Nielsen M. Screening for breast cancer with mammography. Cochrane Database Syst Rev 2001, Issue 4