The concept behind screening for cancer is that earlier detection will lead to more timely and more effective treatment. However, objective analysis tends to reveal that, generally speaking, large numbers of people need to be screen for one life to be saved from the disease being screened for. For example, using mammography as an example, it seems that for every 10,000 women screened over a 20-year period, 43 lives are saved . Mammography is recommended every 3 years in the UK that means it would take about 70,000 mammograms to save those 43 lives. Another way of expressing this is that for one life to be saved, more than 1,600 mammograms must be performed. I am not glib about the lives saved through mammography, but it is clearly not an efficient intervention.
Also, cancer screening comes with some very real risks. The screening procedure itself may pose risks. For example, I recently saw a patient who almost died as a result of a blood borne infection (septicaemia) as a result of a biopsy that was advised as part of a screening for prostate cancer.
Another potential harm can come from ‘false positives’ – tests results that suggest a problem when, in fact, there is nothing wrong. If nothing else, false positives can cause considerable psychological distress for the person who has been screened, as well as maybe people close to them.
The last major cause of potential harm from screening is referred to as ‘overdiagnosis’ – essentially treatment for a cancer that would never have bothered the individual over the natural course of their life.
The British Medical Journal has recently published a review concerning the adverse effects of cancer screening . The study assessed the percentage of studies on screening that quantified the known risks. In all, 198 articles were assessed. Negative ‘psychosocial’ consequences were only reported in 9 per cent of these. The results for false positive results and over-diagnosis were even worse (4 per cent and 7 per cent respectively).
In other words, studies concerning screening rarely quantify its important risks.
It occurs to me that this finding may be symptomatic of the culture in cancer screening, where the focus has traditionally been on the supposed benefits, with little discussion of the potential downsides. There has been a vogue for these potential problems not to be shared transparently with people. As a result, screening is sometimes presented to individuals as a ‘no-brainer’.
This has particularly been the case with mammography, it seems, though more recently the failure for women to be properly informed has been highlighted by some doctors and researchers. As a result. The breast cancer screening leaflet for women in the UK was updated earlier this month. But, already, it has attracted criticism for still not giving women access to vital information .
Susan Bewley, professor of obstetrics at King’s College London, has told the British Medical Journal that the leaflet does not contain crucial information that for every 15 women who are given a diagnosis of breast cancer through screening and who will undergo treatment, only one life will be saved. In addition, though, three women will end up being treated unnecessarily. According to Professor Bewley, the leaflet does not explain the harms of screening and also overlooks the fact that women who undergo it are at increased risk of undergoing unnecessary mastectomy.
Practically everyone I talk to about the limitations and hazards of cancer screening is quite surprised and sometimes even shocked by the facts. I suspect we have a long way to go before the general indoctrination about the ‘benefits’ of cancer screening are balanced with information about its limitations and hazards. But it’s only once someone is fully aware of the facts that they are in a position to judge whether cancer screening is right for them. It most certainly is not a no-brainer it is often presented to be.
1. Hawkes N. Breast screening is beneficial, panel concludes, but women need to know about harms. BMJ2012;345:e7330
2. Heleno B, et al. Quantification of harms in cancer screening trials: literature review. BMJ 2013;347:f5334
3. Kmietowicz Z. New breast screening leaflet still denies women the full picture, says critic BMJ 2013;347:f5735
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Yes, but what are the alternatives to mammography? What would be a more efficient intervention?
John, would screening for prostate cancer parallel the statistics for breast cancer?
Medical Digital Thermal Imaging is a non-invasive method of detecting breast tissue (and many other) problems. It can detect abnormalities 10x earlier than mammography. (Rmembering that early detection is the key to successful treatment outcomes).
It does not use radiation and does not compress the breast tissue at all. Shouldn’t this be used as the initial assessment tool with perhaps mammography as a second stage diagnostic only for those for whom problems are detected?
Doctors have been ignoring the down side for a long time, usually for profit. Involuntarily circumcise a million boys — what ever happened to my body my choice? — and you may prevent one case of cancer in very old age. Some of those boys will die from the mutilation, many will have adheasions that will need to be corrected, and all have to live with reduced sexual pleasure, the scaring, and noting every time you go to the bathroom that some bastard sexually assaulted you. It is child molesting. Doctors think they are unquestionable royality. I never thought I would ever think of a group of “professional” who could possibly be worse than lawyers but doctors are succeeding at that.
Thank you for addressing the downside and risks of cancer screening. I live in the United States and I think Dr. Gilbert Welch is also confronting the medical establishment on issues of over-treatment and unnecessary screening. You guys are my medical heroes! As with any screening test, one should always ask the question of whether or not you would be willing to pursue the recommended treatment. I have come to the conclusion that I won’t follow the prescribed/mainstream or alternative treatment for cancer, osteoporosis, high cholesterol, etc. In other words, I no longer get any screening test and don’t intend to do any in the future. I will also say, without going into my personal drama, that I have been harmed by medical treatment (pharmaceutical drug) so I am very cynical of any treatment.
I do not dismiss anything out of hand, but are you aware of research which shows screening via thermography is effective and reduces the risk of the problems associated with mammography such as false positives and overdiagnosis?
I have not looked at the prostate cancer screening issue recently, but the last time I looked the issue was similarly vexed. I recall the upshot being that it is not effective for saving lives, but this needs checking. Certainly, any argument for prostate cancer screening is not clear-cut (the same as mammography). I don’t believe we even have a national prostate cancer screening programme here in the UK.
Re: Your comment – Yes I am aware of the false positives, mis-diagnosis and over diagnosis of mammography, which was the reason I highlighted the huge benefits of DMTI.
I client of mine who was told by her doctor she had a ‘bad neck’ and was prescribed painkillers but it was obviously more than that. I referred her for Thermal Imaging which revealed claudication and atherosclerosis of the carotid artery.
This technology needs a greater profile.
Keep up the great work Dr John.
Another problem with mammography is that, if you’re slim and small-breasted, it hurts! From this point of view I certainly like the alternative idea of thermography.
I recently refused a mammogram. I have no family history of breast cancer, and an very low risk by all markers.. I noted that my call to the screening centre to tell them that I would not be attending was greeted with absolutely no surprise. I am told that the drop-out rate on second calls is very high, as the procedure is rather unpleasant.
I was much more offended by the pink room and the nurse using the word “boobies” than by the procedure, by the way.
I have also taken to crossing off the cholesterol tests from by blood forms, as I won’t take statins under any circumstances, and I don’t want a Bad Number (!) to cause aggravation.
Lately I won’t let anyone take my blood pressure in any medical setting, as I have really bad White Coat Hypertension (and a meter at home) and I don’t want to be chased by an aberrant 155/90 forever..
Hello Dr. Briffa. Sean Croxton of undergroundwellness.com did a couple of youtube videos highlighting this procedure: