'Most women and many health professionals know little or nothing about the risk of overdiagnosis.' Photo: Sandy Scheltema
A MAJOR public inquiry in Britain into the risks and benefits of breast cancer screening has confirmed that screening programs extend lives - but it also confirmed the existence of overdiagnosis of breast cancer. ''The panel believes that overdiagnosis occurs,'' they wrote in the prestigious medical journal The Lancet. This conclusion should settle a long-standing, acrimonious and deeply contested debate.
The reality of overdiagnosis of breast cancer can be very difficult to accept. It means finding cancers that, without screening, would never be diagnosed. Unlike a ''false positive'', where a suspected cancer is not in fact there, overdiagnosis means there really is cancer present, confirmed by a pathologist looking at cells from a biopsy. But these overdiagnosed cancers don't behave the way we traditionally expect cancers to behave: they don't cause symptoms and they don't kill you. The cause of overdiagnosis is breast cancer screening itself.
At this stage, whether a particular woman might have an overdiagnosed cancer or not is difficult to judge, and therein lays the conundrum at the heart of this issue. Common treatments include surgery, radiotherapy, adjuvant endocrine therapy and chemotherapy, and while you would generally want these treatments for life-threatening cancer, you wouldn't want them for a cancer that's not going to hurt you.
On top of all that there is the psychological and emotional trauma of being diagnosed with cancer, as well as the implications for siblings and children considered at higher risk because of their ''family history''.
Yet most women and many health professionals know little or nothing about the risk of overdiagnosis from attending breast screening programs.
The latest findings about overdiagnosis are doubly important because this is just one example of a potentially much bigger problem, dubbed a ''modern epidemic'' by a leading American medical journal, and driven by many factors.
New technology now enables us to see all kinds of tiny ''abnormalities'' but the clinical importance of some of them just isn't clear, and many are perfectly benign. Doctors have even have coined a tongue-in-cheek term for those picked up by accident: incidentalomas. Other drivers include the fear of litigation if doctors miss something that later turns out to be significant, and commercial interests that are served by maximising the numbers of people tested and treated. Underpinning all this is a deep cultural faith in early detection, and widespread ignorance of the risk of overdiagnosis.
What's required are more reports like the one in The Lancet this week, the result of an independent and comprehensive review of the evidence about breast cancer screening, led by the internationally respected public health professor Sir Michael Marmot.
It concluded that women who are regularly screened reduce their risk of dying from breast cancer by 20 per cent, but have a 19 per cent chance of being overdiagnosed over a 20-year period of screening. In other words, about one in five breast cancers found among regularly screened women represent overdiagnosis.
Noting the uncertainty around these statistics, the panel estimated that for every woman who does not die of breast cancer because of screening, three others are overdiagnosed and overtreated.
Research conducted by Australian epidemiologists - including one of the authors of this article, Alexandra Barratt - and published two years ago, concluded that in New South Wales about one in four cancers among regularly screened women represent overdiagnosis. That study used different methods with different forms of data for a different program, which screens every two years rather than every three as in Britain, but the results are similar.
Other conditions where there are real concerns about overdiagnosis range from ADHD to high blood pressure to prostate cancer.
Overdiagnosis of breast cancer may be awkward for screening services to talk about, but it is fundamentally misleading to not tell women about it. As the British panel wrote: ''Clear communication of these harms and benefits to women is essential, and is the core of how a modern health system should function.''
Alexandra Barratt is a professor of public health at the University of Sydney. Ray Moynihan is a senior research fellow at Bond University.