Following recent controversy about the pros and cons of breast screening, a new study part-funded by Cancer Research UK found that breast screening saves two lives for every case of over-diagnosis.
The study by scientists at Wolfson Institute of Preventive Medicine at Barts and the London School of Medicine and Dentistry, is about to be published in the Journal of Medical Screening.
Overdiagnosis of breast cancer has been in the news a lot because recent reports suggest that for every life saved, six women were overdiagnosed: that is they underwent treatment for cancers that would otherwise probably never have been diagnosed during their lifetime. This questioned whether the benefits of screening were outweighed by the harms.
But the researchers who did this latest study believe it is worth going for screening because their figures show the benefits outweigh the harms.
Lead author Dr Stephen Duffy, Professor of Cancer Screening at the Wolfson Institute of Preventive Medicine, told the media that:
Unfortunately, we haven’t yet got a flawless screening test, and some cases that are picked up wouldn’t have needed treatment.”
“But for every case like this, screening saves two women who would have otherwise died from breast cancer,” he added.
However, he also said that if screening show a tumor is present, then it is important to fully consider the range of options available before starting treatment.
“Women should be given the opportunity to understand the implication of their screening results and discuss their treatment options with a specialist,” said Duffy.
For their research, Duffy and colleagues actually conducted two studies. In the first study they estimated the number of women in the UK who would have died from breast cancer if breast cancer screening had not been brought in, and in the second study they compared breast cancer deaths among women who were and women who were not offered screening in a randomized trial involving 80,000 women in Sweden.
The results showed that over a 20-year period in England, for every 1,000 women screened, 5.7 breast cancer deaths were averted. At the same time, for every 1,000 women screened, 2.3 were told they had a tumor but it was not clear how aggressive it was.
This equates to 2.5 lives saved and one case of over-diagnosis for every 28 cases diagnosed, according to a BBC report on the study.
Media reports suggest at least one expert is not happy with the way the researchers analysed the data. Jayant Vaidya, a breast cancer surgeon at University College London and the Whittington Hospital describes the calculations as “opaque”. He told the BBC that:
“Women who go for breast cancer screening need to know that there’s a good chance they could be diagnosed with a cancer which is not harmful and may never have bothered them.”
But Dr Lesley Walker, director of cancer information at Cancer Research UK, said that The National Breast Screening Programme saves lives and that is why they encourage women to go when they receive their invitation.
“All women should have access to high quality information and advice to help them make decisions that are appropriate to their individual condition,” she said in a statement.
Walker said it was “standard practice” for women to have the discussions that help them make choices that are right for them, and that women should not be worried about overdiagnosis as a reason not to attend screening.
“As well as attending screening, we would encourage all women to be breast aware and to go to their doctor if they notice any unusual changes to their breasts,” urged Walker.
“Absolute Numbers of Lives Saved and Overdiagnosis in Breast Cancer Screening, from a Randomised Trial and from the Breast Screening Programme in England.”
Duffy et al, Journal of Medical Screening, 2010.
Sources: Queen Mary, University of London; Cancer Research UK, BBC.
Written by: Catharine Paddock, PhD