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Do we have an overdiagnosis problem in mammography screening programmes for early detection of breast cancer in asymptomatic women? The question is more urgent than ever now that the U.S. Preventive Services Task Force changed its recommendation for the starting age for mammography screening from 50 to 40 years. We've met Karsten Juhl Jørgensen (Department of Clinical Research - Københavns Universitet, Cochrane Denmark) a the meeting Medicine & the Media in Florence.
Do we have an overdiagnosis problem in mammography screening programmes for early detection of breast cancer screening in asymptomatic women?
(Editor's note, read here : overdiagnosis)
Yes, so overdiagnosis is a really an unavoidable problem with basically all types of screening.
And it has to do with the fact that people die from all sorts of causes apart from the disease that we're screening for. So if you detect that disease early, there is a risk that people will die from something else before this disease that you screen for would develop into something serious.
Another reason is that when you screen for a disease, you often detect a different type of disease than what you do when you detect symptoms in patients and then make a diagnosis.
So we know that many diseases including breast cancer, is not just a single entity. We're dealing with diseases that span a spectrum, various degrees of severity.
(Editor's note, read here : cancer development)
And that, if we screen, because the least aggressive cancers takes the longest time to develop, those are predominantly the ones that we are going to find with screening.
This simply because there is more time to detect them.
All the aggressive tumors, those that most often kill people develop quickly.
So they fall through the mesh of our screen and are not detected by screening but pops up between screening rounds.
So those are one of some of the well-known limitations of cancer screening. So this is called length bias, the longer you have to detect the cancer, the more you'll detect.
And it contributes to overdiagnosis because the slowest least aggressive cancers are predominantly the ones that are overdiagnosed, but they're still cancers
So they're still treated and people still become cancer patients with all the implications that this has for their well-being. So we know that breast screening and many other types of screening they have harms, just like any other medical intervention has harms.
That's really the only thing we can be sure about any intervention. Any treatment it always has harms so the question is then if these harms are outweighed by the benefit. And that's one question if we're talking about patients that comes to us as doctors seeking treatment.
They’re seeking help with the problem that they feel that they have .
Then we have a responsibility to do our best to help these patients, even if we might not have a complete understanding a complete knowledge about the effects of the interventions that we could use.
But if as a society we choose to go out and offer a screening program to a healthy population, there's a completely different obligation on us to know what we're doing for sure.
So we have been worrying about new recommendations to expand breast cancer screening for age groups where the evidence is really uncertain.
There's uncertainty about the effects of breast screening for all age groups, but they're particularly large for women in their 40s and for women over 70 years of age.
That's why we haven't screened those age groups for many decades in many countries.
But recently, new recommendations came out from the US preventive Services Task Force recommending breast screening for women in their 40s, and we were worried about that because really the foundations for that recommendation were different from what we're used to see from the US preventive Services Task Force.
(Editor's note, read here: lowering the age of screening?)
They have usually been a flagship for evidence-based medicine methods and has been a really trusted organization but in this particular instance, rather than trusting the evidence that we do have from randomized trials and which we've known about for years they have chosen to do model calculations and base their recommendations on those.
And that's really deviating from some of the fundamental principles of evidence-based medicine and we find that worrying because if you base your recommendation on models you're more likely to make mistakes.
All models are based on assumptions, not knowledge, it's like the weather forecast and models cannot always be trusted. So that's a worry, it's a worry both because we might make a wrong decision and harm people through screening, but also because it deviates resources from things we really know works.
And if we look at breast cancer mortality in women over 40, we are really seeing a very positive development where the risk of dying from breast cancer for woman in her 40s has been cut in half over the past 30 years without screening.
(Editor's note, read here: risk of death)
So we've become much better at treating women, young women with breast cancer which of course is an incredible success story, that we should really be proud of as a profession.
And we should praise the oncologists through a responsible for this very positive development.
But at the same time it also means that there has never been less reason to start screening women in their 40s because we are already doing much better than we ever have before in history, really towards this disease.
So there is no crisis in a breast cancer in women in their 40s, we're doing very well and in my opinion we need to be certain that if we're going to do more and invite these women to screening, we don't end up doing more harm than good.