Is breast cancer screening actually saving lives?
A Norwegian study, published in BMJ, has looked at the effectiveness of modern mammography screening by measuring breast cancer mortality among screened and unscreened women. The authors found that an invitation to mammography screening was associated with a 28 per cent reduced risk of death from breast cancer compared with not being invited to screening.
That means that for every 10,000 women invited to screening, about 27 deaths from breast cancer might be avoided during their lifetime. The authors describe this benefit as a”substantial effect”.
However, an accompanying editorial from US researchers states, “The Norwegian study largely confirms what is already known: the benefits of screening mammography are modest at best. While the benefits are small, the harms of screening are real and include overdiagnosis, psychological stress, and exorbitant healthcare costs.”
The editorial authors call for women to be given balanced information to help them make informed decisions about screening.
The SMC collected the following expert commentary.
Belinda Scott, medical adviser to the NZ Breast Cancer Foundation, comments:
“The study shows a definite reduction in deaths when women are screened, and that reflects what we’ve seen throughout the world.
“It’s important for women to understand that screening does have risks, and to be able to opt out, but we do have a strict, well-monitored screening programme here through BreastScreen Aotearoa.
“It would interesting to undertake a similar study of mammography benefits in New Zealand – much of the data used in the Norway study is available in the breast cancer patient registers funded by the NZBCF and it would be great to see that used to gain insights into the effectiveness of our own screening programme.”
Our colleagues at the AusSMC collected the following expert commentary.
Terry Slevin, Director of Education and Research at the Cancer Council, WA, comments:
“Mammographic screening for breast cancer has been a little more controversial in the northern hemisphere than it has been in Australia. There is no perfect screening program and no perfect screening test. This study is consistent with what we have thought to be the benefits of breast cancer screening in Australia. This study confirms that there are about 28 per cent fewer breast cancers deaths when screening is offered. Importantly there are 37 per cent fewer deaths for those who participate in screening (not everyone who is invited participates). The price women pay for participating in a screening program is that some are treated for conditions that may not have turned into aggressive life threatening cancers. This is referred to as overtreatment. Women should be aware of this fact.
“Early detection through screening is one of the tools we use to tackle breast cancer but prevention is important too. By reducing or avoiding alcohol consumption, being a healthy weight, being more physically active and avoiding or minimising Hormone Replacement Therapy, women can reduce their chance of being diagnosed with breast cancer in the first place. And of course advances in treatment have been beneficial. It is worth noting we still lose about 3,000 women each year to breast cancer in Australia each year. So when it comes to screening – it is not perfect and there are some down sides, but it still remains an important arrow in our quiver when it comes to tackling breast cancer.”
Professor David Currow, Chief Cancer Officer and CEO at the Cancer Institute, NSW, comments:
“While this robust study shows a 28 per cent reduction in breast cancer mortality among women who are invited to screen, what is perhaps more important is that the study is able to pick out the actual benefit of participation, a 37 per cent reduction in mortality for women who participate in the screening program. This reinforces the importance of keeping participation rates high, and should encourage more women to screen.
“The editorial accompanying this study describes the effect of screening as “modest” but if we were talking about a new treatment, a 28 to 37 per cent reduction in mortality would be seen as a great step forward.
“At the end of the day, this study adds to the wider body of evidence that population based screening for breast cancer continues to save lives in our community.”
(Note: The Cancer Institute in NSW holds responsibility for all screening in that state)
Professor Anne Kavanagh is the Director of the Gender and Women’s Health Unit in the Melbourne School of Population and Global Health at the University of Melbourne, VIC. Professor Dallas English is the Director of the Centre for Molecular, Environmental, Genetic and Analytic Epidemiology in the Melbourne School of Population and Global Health at the University of Melbourne, VIC. They comment:
“The authors attempted to replicate a randomized trial (which is the gold standard study to evaluate screening) by basing their analysis on invitations for screening not whether women participated. The 28 per cent reduction in mortality they observed is slightly greater than the 20 per cent reduction reported from the old randomized trials of screening. In 2009, there was a major evaluation of the Australian BreastScreen program; it found that current participation rates were associated with between a 21 per cent and 28 per cent reduction in mortality. Last year, we published a study using data from BreastScreen Western Australia, which showed that women who attended for screening had a 50 per cent lower breast cancer mortality. We carefully controlled for potential differences between women that attended and did not attend for screening that might explain the findings. We also combined the results of all studies using the same design – and this also showed a 50 per cent reduction. The results of all these studies consistently show that invitation to attend is associated with a modest reduction in mortality and that attendees have a greater reduction.
“There are some potential downsides of screening, particularly ‘overdiagnosis’ – some women receive a diagnosis of breast cancer through screening that would not become apparent in their life time. The extent of this problem is debated. It is critical that we obtain good evidence about this from Australian programs – work we are currently conducting. Evidence from the Australian program may then be used to provide women with information about the harms and benefits of screening.”