The controversy over the risks and benefits of cancer screening has been given renewed impetus with the publication of a letter to the editor of the Times of London concerning breast cancer screening. Since this letter is not available online to non-subscribers, it is worth quoting at some length:
“…there is evidence to show that up to half of all cancers and their precursor lesions that are found by screening, if left to their own devices, might not do any harm to the woman during her natural lifespan. Yet, if found at screening, they potentially label the woman as a cancer patient: she may then be subjected to the unnecessary traumas of surgery, radiotherapy and perhaps chemotherapy, as well as suffer the potential for serious social and psychological problems. The stigma may continue to the next generation as her daughters can face higher health insurance premiums when their mother’s overdiagnosis is misinterpreted as high risk. We believe that women should be clearly informed of these harms in order to make their own choice about whether to attend for screening.
“The subject has now come to a head with the publication in the next issue of the British Medical Journal of Breast screening: the facts – or maybe not by Peter C. Gotsche and his colleagues from the independent Nordic Cochrane Collaboration Center. They describe a synthesis of published papers that quantify the benefits and harms of screening using absolute rather than relative numbers that make it easier to comprehend. They conclude as follows: if 2,000 women are screened regularly for ten years, one will benefit from the screening, as she will avoid dying from breast cancer. At the same time, ten healthy women will, as a consequence, become “cancer patients” and will be treated unnecessarily. While there is debate about exactly what these numbers are (some data shows more women benefit and fewer healthy women treated unnecessarily) the overall picture is clear.
“The most disturbing statistic is that none of the invitations to screening come close to telling the truth. As a result, women are being manipulated, albeit unintentionally, into attending…”
The letter was signed by four physicians and patient advocate Hazel Thornton. The paper they referred to, by Gotsche and his colleagues, is available here. It draws heavily on a meta-analysis by Gotsche and M. Nielsen, published by the Cochrane Collaboration and available here.
The fact is, women have been preposterously oversold on the benefits of breast cancer screening. A telephone survey of women in four countries published in the International Journal of Epidemiology found that the majority of women surveyed believed that reduces or eliminates the risk of contracting breast cancer (it does nothing of the sort). A whopping 94% overestimated the reduction in the risk of dying of breast cancer by a factor of at least 20 times, and a majority overestimated it by a factor of at least one hundred.
Even that doesn’t tell you the whole story. If you think a one in two thousand reduction in the risk of dying of breast cancer can even be measured reliably, well, bully for you. But we all have to die of something. What difference does it make if you die of breast cancer, or you die from another cause, at the exact same time? The only statistic that means anything to you as an individual is the reduction in mortality from all causes. And the same meta-analysis by Gotsche and Nielsen shows that women who were screened for breast cancer and those who were not had EXACTLY THE SAME DEATH RATE.
Meanwhile, the negative effects of breast cancer screening are consistently underplayed, or ignored completely. Any mention of the negative aspects is usually confined to the transient pain and discomfort of mammography – far and away the least important negative aspect. As this article in the New York Times makes clear, a diagnosis of cancer can ruin your life. It can bankrupt you, it can make you permanently unemployable, it can prevent you from ever obtaining health insurance. Furthermore, being treated for cancer can kill you. Check out this article in Lancet Oncology which shows that radiation therapy for breast cancer can dramatically increases a woman’s risk for cardiac mortality and lung cancer.
There is another cost, one which I don’t know how to measure, but which I am sure is there nonetheless. The fact that the placebo effect exists and must be controlled for in every clinical trial shows that we have tremendous power to make ourselves well – or, one would assume, to make ourselves sick. What does that say for the medical industry’s relentless efforts to make us all think of ourselves as disease-ridden time bombs?
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