By Emily Caulkett-
Breast screening is not overdiagnosed in the Uk, experts at Queen Mary university have said as they seek to quench fears about overscreening.
Researchers from Queen Mary University of London and King’s College London , funded by the National Institute for Health and Care Research, have set out to examine the levels of overdiagnosis linked to the screening programme.
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Their new study, published in the journal Cancer Medicine, examined 57,493 cases among women who attended screening in 2010 and 2011, and compared this to cases among more than 100,000 women who did not attend screening. It concluded that the level of breast screening in the Uk is at normal levels and not overdiagnosed as previously feared.
Evidence from several trials in the past show that mammography screening reduces the risk of death arising from breast cancer, but those studies have also provided sufficient evidence that overdiagnosis represents a serious harm from population breast screening Regular mammograms are the best tests doctors have to find breast cancer early, sometimes up to three years before it can be felt.
The outcomes of screening, reduction of deaths resulting from breast cancer and overdiagnosis have been shown to vary between studies conducted by researchers. The trade-off between the benefit and the collective harms of BC screening, including false-positives and overdiagnosis is more finely balanced than initially recognized, however the snapshot of evidence presented on overdiagnosis does not mean that breast screening is worthless.
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The researchers from Queen Mary University estimated the effect of screening on breast cancer risk, and the results were combined with national incidence data to estimate absolute rates of overdiagnosis. Overdiagnosis was calculated as the cumulative excess of cancers diagnosed in women aged 50-77 attending three-yearly screening between ages 50 and 70 compared with women attending no screens.
The estimated number of cases of overdiagnosis in women attending all screens in the programme was just under 3 per 1000, corresponding to an estimated 3.7% of screen detected cancers overdiagnosed.
This is considerably lower than has been suggested in the past. Authors conclude that the NHS Breast Screening Programme is associated, at worst, with modest overdiagnosis of breast cancer.
The detection of tumours in patients can lead to much distress once it is brought to their attention. In such cases, a “harmless” tumour will be treated unnecessarily, which is called overtreatment, often involving therapies that have their own risks or significantly reduce the quality of life.
Overdiagnosis refers to the diagnosis of a medical condition that would not have produced any symptoms or problems had it been left undiagnosed. Overdiagnosis has risen sharply with the use of screening tests nowadays, because of the importance laid on detecting potentially deadly or curable illnesses before they produce symptoms.
The unexpected fallout of this has been the detection of other abnormalities that are not going to create symptoms if left untreated. Overdiagnosis could include, for instance, the detection of indolent tumours that typically grow so slowly that the individual dies of old age without ever knowing about the presence of the tumour.
Concerns over the risk of overdiagnosis prevents some women from taking up the offer of screening
Overdiagnosis was calculated as “the cumulative excess of cancers” diagnosed among the screening group compared to those who did not go to their screening appointments.
An estimated 3.7% of screen-detected cancers were “overdiagnosed” – lower than previous estimates.
The research is consistent with a separate research conducted in Denmark. When the screening was introduced, the assessment was that around twenty per cent of the deaths from breast cancer among those screened could be averted. While this corresponded to approximately 220 deaths a year in Denmark 25 years ago, today the number has been halved.
The study shows that in 1996, it was necessary to invite 731 women to avoid a single breast cancer death in Norway, you would have to invite at least 1364 and probably closer to 3500 to achieve the same result in 2016.
Superfluous Diagnosis
“One in five women aged 50-70, who is told they have breast cancer, has received a ‘superfluous’ diagnosis because of screening — without screening, they would never have noticed or felt that they had breast cancer during their lifetime,” says the researcher.
Up to 900 women annually in Denmark fall under the one in five category. In addition, every year more than 5000 women are told that the screening has given rise to suspicion of breast cancer — a suspicion that later turns out to be incorrect.
The authors concluded: “Our results showed little if any overdiagnosis, and it is reasonable to conclude that NHS Breast Screening Programme is associated with at worst modest overdiagnosis of breast cancer.”.
In the UK, breast cancer accounts for 31% of all new cancers diagnosed in women each year, with cases having increased by 4% in the last decade. Despite the rise in cases, deaths caused by breast cancer are declining. This is in part due to early diagnosis of breast cancer through the NHS Breast Screening Programme.
The NHS Breast Screening Programme invites anyone registered with a GP as female aged 50-70 for a screening every three years. Breast cancer screening uses x-rays called mammograms to check breasts for signs of cancer.
The benefits of screening has long been dogged by the problem of overdiagnosis because many times a real cancer which grows so slowly that it would never have led to any symptoms or deadly consequences.
Estimates of overdiagnosis have varied widely, ranging from less than 5% of screen detected cancers to more than 30%. When a cancer is diagnosed, we cannot tell whether it is overdiagnosed or not, so all cancers need treatment. It is important for women to have reliable estimates of overdiagnosis in order to make an informed decision on whether to be screened or not.
They estimated the effect of screening on breast cancer risk, and the results were combined with national incidence data to estimate absolute rates of overdiagnosis. Overdiagnosis was calculated as the cumulative excess of cancers diagnosed in women aged 50-77 attending three-yearly screening between ages 50 and 70 compared with women attending no screens.
Stephen Duffy, Professor of Cancer Screening, Queen Mary University of London and joint lead investigator, said:
“These results provide some reassurance that participation in the NHS Breast Screening Programme confers only a low risk of an overdiagnosed breast cancer. Along with the results of our previous study of the effect of screening on breast cancer mortality, this indicates that the benefit of screening in preventing deaths from breast cancer outweighs the small risk of overdiagnosis.”
Peter Sasieni, Academic Director of the Clinical Trials Unit and Professor of Cancer Prevention at King’s College London, and joint lead investigator, said:
“Overdiagnosis is quite a complex issue. Had we stopped following women at age 70, nearly 1% of screened women would seemingly have been overdiagnosed, but by waiting another 7 years, more never-screened women will be diagnosed with breast cancer and the three-quarters of the excess cancers turn out to have been diagnosed early rather than overdiagnosed. What this means is that most previous studies have overestimated the harms of participating in breast cancer screening up to the age of 70.”
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