Mammography is a widely advocated and popular intervention designed to pick up breast cancers earlier than they would otherwise be, and therefore allow less invasive and more effective treatment. However, as I pointed out in a blog back in 2007, some researchers believe that the benefits of mammography are somewhat overblown, and that the potential downsides are at the same time downplayed or not mentioned at all. A major problem with mammography is that it may detect cancers that would not go on to trouble women during their lifespan. This can obviously subject women to unnecessary stress and anxiety, not to mention unnecessary treatment in the form of, say, surgery, radiotherapy and chemotherapy.
The debate about the relative benefits and harms of mammography has reared up again in the UK because of the publication of a letter in the Times newpaper which can you read here. In it, 23 interested parties cite evidence that is published by the researcher Peter Gøtzsche and his colleagues from the independent Nordic Cochrane Centre in 2006 [1]. This review of the available literature concluded that: for every 2000 women invited for screening throughout 10 years, one will have her life prolonged. In addition, 10 healthy women, who would not have been diagnosed if there had not been screening, will be diagnosed as breast cancer patients and will be treated unnecessarily. It is thus not clear whether screening does more good than harm.
The letter in the Times appears timed to coincide with the print publication of an article by Peter Gøtzsche and colleagues in this week’s British Medical Journal [2]. The article outlines some of the apparent deficiencies and omissions in the information given to UK women regarding breast screening. The article refers to the UK Department of Health (DoH) leaflet entitled ‘Breast Screening; the Facts’. The authors of the article make the point that the title of the leaflet suggests the information can be trusted. But can it?
The authors of the BMJ piece make the point that the DoH leaves no doubt that screening is good for women, and quote excerpts from the leaflet which include: “Why do I need breast screening?”, “If changes are found at an early stage, there is a good chance of a successful recovery,”. The leaflet also claims that breast screen saves “an estimated 1400 lives each year in this country” and “reduces the risk of the women who attend dying from breast cancer.”
However, according to the authors, the leaflet has many deficiencies which mean that women cannot make informed decisions about whether they attend breast screening or not.
For instance, no mention is made of the major harm of screening”that is, unnecessary treatment of harmless lesions that would not have been identified without screening. It is in violation of guidelines and laws for informed consent not to mention this common harm, especially when screening is aimed at healthy people. The new guidelines from the General Medical Council state: “You must tell patients if an investigation or treatment might result in a serious adverse outcome, even if the likelihood is very small.” The likelihood of being overdiagnosed after mammography is not very small; it is ten times larger than the likehood [sic] of avoiding death from breast cancer.
The leaflet notes that about one in every 20 women screened will be recalled for more tests because of ‘false positive’ results (results that suggest a problem when, in reality, there is none). But, as Gøtzsche and colleagues point out, the more screenings a woman has, the more likely she is to end up with a false positive result. They cite evidence that shows that after 10 screens, risk of false positive diagnosis was 50 per cent in one piece of research and 20 per cent in another. The authors add: We now know that the psychosocial strain of a false alarm can be severe and may continue after women are declared free from cancer.
Basically, mammography can lead to women have unnecessary treatment including radiotherapy. Gøtzsche and colleagues point this out, and also explore some of the risks associated with this. They note that the leaflet tells women that the dose of radiation from mammography is very small, but does not tell women of the risks associated with healthy women having radiotherapy. They cite evidence that radiotherapy suggesting that radiotherapy may double the risk of death from heart disease and lung cancer. The authors that that Technological improvements may have diminished these harms to some extent, but they are still important.
The authors also tell us that the leaflet summary implies that screening leads to fewer mastectomies. In fact, research shows that screening leads to 20 per cent more mastectomies being performed.
Also, we are told that the leaflet expresses no reservations about screening older women, only a scare that the breast cancer risk increases with age, although it has not been shown that screening these women decreases their risk of dying from breast cancer. Furthermore, the problem with overdiagnosis becomes more pronounced, and the likehood of gaining any benefit smaller, due to competing risks of death.
And, finally, the authors point out that it has not been proven that screening saves lives. While it may reduce the risk of breast cancer mortality (by about 15 per cent), studies show that breast screening does not decrease total cancer mortality. As the authors point out This indicates that the benefit of screening is likely to be smaller than generally perceived.
The authors then conclude: We believe that if policy makers had had the knowledge we now have when they decided to introduce screening about 20 years ago, when nobody had published data on overdiagnosis or on the imbalance between numbers of prevented deaths from breast cancer and numbers of false positive screening results and the psychosocial consequences of the false alarms, we probably would not have had mammography screening.
This is one group of reseachers’ view, and not everyone will share it. The figures regarding those that benefit and those who may come to harm have been disputed. However, there can be little doubt that many women are simply not being informed of the full facts about breast screening. So one figure I think we can be certain of is that chances of these women making a truly informed decision about mammography is zero. I’m not against mammography, but I am against women being kept in the dark about the true benefits and risks associated with this practice.
References:
1. Gøtzsche PC, Nielsen M. Screening for breast cancer with mammography. Cochrane Database of Systematic Reviews 2006, Issue 4. Art. No.: CD001877. DOI: 10.1002/14651858.CD001877.pub2.
2. Gøtzsche PC, et al. Breast screening: the facts”or maybe not. BMJ 2009;338:b86
