Friday September 7 2012
Screening is recommended for all women aged 50 to 70
“Breast cancer screening ‘works and we should move on’,” is the slightly confusing headline of The Daily Telegraph. It says that a new study shows that the risk of dying from breast cancer is halved in women who undergo mammography screening. The newspaper rather prematurely claims that this “draws a line under the controversy”.
The Australian study looked at the mammography screening history of 427 women who had died from breast cancer, and compared this with the screening history of a group of healthy women. They found that women who died from breast cancer were less likely than healthy women to have participated in screening programmes.
The researchers also carried out a meta-analysis of similar types of studies (known as case-control studies). They found similar results – that the risk of dying from breast cancer was reduced by just less than half (49%) in those who participated in screening.
Screening for breast cancer is a controversial issue, with supporters highlighting the fact that early diagnosis leads to an improved chance of a successful cure. It is estimated that the NHS Breast Screening Programme saves 1,400 lives a year. Critics have argued that screening has an unacceptably high false positive rate. This means that some women who do not have breast cancer are wrongly diagnosed as having the condition. This causes harm through worry, unnecessary further invasive tests and sometimes treatment that is not needed.
Overall, the study adds to the body of evidence suggesting that the benefits of breast cancer screening do outweigh the risks, improving the outlook for women with breast cancer.
Despite the Telegraph’s claim that a line has been drawn under the controversy, it would be surprising if there were no continuing debate on the pros and cons of breast cancer screening.
Where did the story come from?
This study was conducted by researchers from the University of Melbourne, Australia, and was supported by a project grant from the National Health and Medical Research Council of Australia.
The study was published in the peer-reviewed medical journal Cancer Epidemiology Biomarkers and Prevention.
The Telegraph provided a largely well written and accurate summary of the research.
What kind of research was this?
This was a case-control study looking at the mammography screening history of women who had died from breast cancer (the ‘cases’) and comparing it with the screening history of a group of healthy women (the ‘controls’). This is one appropriate study design to look at the question of whether breast cancer screening reduces breast cancer mortality.
A randomised controlled trial would be able to take into account the effect of potential confounders, such as other health factors or lifestyle behaviours that may influence both screening attendance and cancer risk. However, this type of trial would be unethical now that the benefits of breast cancer screening have been established.
The researchers say that earlier randomised trials of mammographic screening for breast cancer showed that screening reduces breast cancer mortality by about 25%.
The results of this particular research are strengthened because the researchers also conducted a systematic review and pooling their results in a meta-analysis. The researchers identified additional studies and pooled their results, to see how they compared with the findings of other similar studies.
What did the research involve?
This is a review of the BreastScreen Australia Program (similar to the current UK programme), which currently invites women aged 50 to 69 to attend mammography screening. The population of study for this research was all women on the Western Australia electoral roll between 1995 and 2006, who were 50 or older during that period. To identify women who had died from breast cancer they linked data from the electoral roll to:
- BreastScreen Western Australia screening records
- the Western Australia Cancer Registry (which routinely links cancer diagnoses to the national death registry)
The ‘cases’ examined by the researchers were 427 women who died from breast cancer between the study period, 1995 and 2006. For each case, 10 randomly selected control women were chosen from the source population. These women were:
- matched for age
- resident in Western Australia at the time of the case’s diagnosis
- alive on the date that the case died
Controls were not excluded if they had a breast cancer diagnosis.
Women in each case-control matched group were defined as having received screening if they received mammography screening from BreastScreen at any time between their 50th birthday and the date that the particular ‘case’ received their first diagnosis of breast cancer.
The researchers calculated the odds of participating in screening in women who had not died from breast cancer compared with those who had died. Analyses were adjusted for confounders including socioeconomic status and remoteness of place of residence from health services.
To find additional evidence, the researchers also conducted a review of literature databases in order to identify additional case-controls or observational studies examining the effects of mammography screening. They found nine relevant studies.
What were the basic results?
Overall, the researchers found screening was more common among the controls – 56% of control women had attended screening (2,051 of 3,650) compared with 39% of cases (167 of 427). They calculated that women who took part in the breast cancer screening programme had a 52% reduced risk of dying from breast cancer (odds ratio 0.48, 95% confidence interval 0.38 to 0.59).
The pooled results of the nine additional studies found through their literature review similarly found that women who took part in the breast cancer screening programme had a 49% reduced risk of dying from breast cancer (odds ratio 0.51, 95% confidence interval, 0.46 to 0.56).
How did the researchers interpret the results?
The researchers conclude that their findings suggest that the risk of dying from breast cancer is halved among women who take part in breast cancer screening.
They say that the findings “provide robust and consistent evidence that screening benefits women who choose to be screened”.
This is well-conducted research examining whether participation in an Australian screening programme, which is similar to the current UK programme, reduces the risk of dying from breast cancer. The researchers found that women who participated had a 52% reduced risk of dying from breast cancer. The findings are particularly strong because the researchers carried out a literature search to identify nine additional studies. These found very similar results – overall a 49% reduced risk of dying from breast cancer for those who attended screening.
These observational studies of the effectiveness of screening do, nevertheless, contain some limitations. It is not possible to account for all of the other health and lifestyle factors that might influence both a person’s likelihood of attending for screening, and their risk of developing and dying from the condition.
The researchers have adjusted for socioeconomic status but cannot take into account all the factors that may be having an influence. For example, it is possible that women with generally unhealthier lifestyle behaviours, such as poorer diet or smoking, may be less likely to participate in screening and be at higher risk of dying from breast cancer.
Screening programmes for any condition also always mean weighing up a balance of risks against benefits. The benefits of breast cancer screening appear clear – earlier diagnosis and improved chance of successful curative treatment and survival. Yet there are some risks of breast cancer screening. The risks include issues such as false positive results, with women undergoing further follow-up and investigation, and all the anxiety that entails, for non-cancerous conditions. This research has not conducted a full appraisal of the benefits against the drawbacks of screening but, overall, the study adds to the body of evidence suggesting that the benefits of breast cancer screening outweigh the risks, improving the outlook for women with breast cancer.
The advice in the UK remains the same. Currently, women aged between 50 and 70 are invited to attend breast screening every three years. The programme is gradually being extended to include women aged 47 to 73.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on twitter.