A Woman is Prepared for a Mammogram
Should You Attend Breast Screening?
If you are a woman of 50 or over (or in some countries 40 or over) and live in the developd world, you are likely to receive from a health department or organization an invitation to attend breast screening for breast cancer using mammography.
A mammogram, or mammography, is a technique used in screening for breast cancer which utilizes X-rays to try to detect breast cancer before a lump can be seen or felt. The aim is to treat cancer at an early stage, when a therapy is more likely to succeed.
Mass breast screening programmes are directed at an asymptomatic population, presumably healthy. Women need to make the decision individually of whether to attend, and for that they need information. What we say in this article refers to mammography screening as a mass breast cancer screening programme and does not extend to the use of mammography per se in individual cases.
The first thing is to dispel the myth that breast screening prevents breast cancer, as is often believed. The theory behind screening is that it should discover an already existing cancer as early as possible.
Government's health departments, cancer charities, and concerned people or celebrities like Sir Paul McCartney, whose wife Linda died of breast cancer, advise women to take the test.
Mammography breast screening has advantages and disadvantages. The information pack accompanying the invitation to a mammogram, as well as your doctor, will likely say that its benefits outweigh its costs. Let's examine whether this is so.
The expected benefit is one: saving lives. The possible costs are several: false positives, that is being told you have breast cancer when you don't; being called back for further tests, more or less invasive, like breast biopsies and further mammograms; false negatives, that is being falsely reassured that you don't have breast cancer when you do; being diagnosed with Ductal Carcinoma In Situ (DCIS), a pre-cancer condition which has not spread and nobody can predict whether it will become invasive or not, but all diagnosed cases are subjected to breast cancer treatment, including partial or total removal of breast, radiotherapy and chemotherapy; for women of old age, being diagnosed with another type of nonprogressive breast cancer, a tumour which progresses so slowly that the women will die before the disease can kill them but will nevertheless undergo traumatizing and painful breast cancer treatment without any benefit; getting breast cancer from the exposure to X rays in the mammogram.
To assess the weight and importance of all these possible outcomes we need to quantify them, see how often they occur and in what age group.
Randomised trials comparing mortality rates and other outcomes of women attending breast screening with those of non-screened women over several years have been performed and subjected to systematic reviews.
You can see the results in detail and the sources in Mammography. The main results of the reviews, summarized here, are:
- According to the evidence, for women under 50 breast screening has no benefits, only possible harms.
- For women aged 50 or over the trial results are more controversial. According to previous reviews of the evidence, 1 woman for every 270 screened in this age group will have her life saved from breast cancer. But more recent reviews have concluded that the most reliable trials are those that show no mortality reduction even for women of 50 or over; if all trials are pooled, 1 woman for every 2000 screened for 10 years will have her life prolonged.
- For every 2000 women screened regularly for 10 years, 10 healthy women will be diagnosed with breast cancer and treated unnecessarily: 4 of them will have a breast removed (mastectomy), 6 will undergo breast-conserving surgery (lumpectomy or quadrantectomy, ie a quarter of the breast removed ), and most will receive radiotherapy.
- For every 2000 women screened for 10 years, over 200 women will receive false positives and as a consequence will experience severe distress for months.
- For every 2000 women who participate in 10 rounds of screening, 500 will be recalled for more emaminations because cancer is suspected; about 125 will have a biopsy.
- For every 100 women with breast cancer, 80 to 95 will be correctly diagnosed, but the other 5 to 20 will be falsely reassured by a negative result. The younger the women the higher the rates of false negatives.
- For the effect of mammography radiation in inducing breast cancer, we can only rely on indirect estimates. For every 10,000 women who attend screening starting at 40, 2 to 4 will develop radiation-induced breast cancer and 1 of them will die of it. The best predictor is age at exposure: the older the woman the lower the risk.
- Screening can provide false reassurance. Up to half of all breast cancers among women participating in screening programmes are detected between two screening sessions, and these interval cancers are the most dangerous.
- A mammogram is painful for about a third of women.
Notice that the probability of being overdiagnosed due to mammography is not so small: it is 10 times higher than the probability of avoiding death from breast cancer.
The stress caused by false alarms also should not be underestimated: in a survey on breast screening, women described it as "the worst time in my life". False positives don't just mean anxiety, they also lead to recalls and possible biopsies removing of breast tissue. On the other hand, the wrong reassurance from a false negative result can delay diagnosis of a real cancer.
It seems that with breast screening we have a dramatic positive effect, the saving of lives, at most for a tiny proportion of women screened, and greatly damaging, if less dramatic, effects for a bigger proportion of people. Very difficult to compute the two and calculate or assess the benefits/costs ratio.
In my opinion, far from the benefits outweighing the costs, we have a situation in which the two are finely balanced against each other, and it's hard to tell which ones are greater.
Breast Cancer Risk Factors
It is up to the individual woman to choose whether to undergo a mammogram or not. In the current uncertainty, one criterion for the choice can be to estimate one's own risk of developing breast cancer, and based on that estimate decide: if the risk is high, there is more reason for attending breast screening.
The main risk factors for breast cancer are the following. Age: women of 50 and over are at greater risk, which is why in the randomised trials breast screening under that age has shown no benefit at all, only costs - see below; genetic predisposition: if a close relative has had breast, ovarian, uterine or colon cancer, the risk is higher; being overweight, smoking, alcohol drinking all increase the risk; childbirth: women who had a child at 30 or under are more protected than women who had children later or never, and having more than one pregnancy reduces the risk; age at menarche (first period): the younger, the higher the risk; age at menopause: the older, the higher the risk; Hormone Replacement Therapy (HRT) with estrogen: having received it for several years increases the risk; radiation: having received it as a child or young adult as therapy for cancer of the chest area much increases the risk, the younger the start of radiation therapy and the higher the dose the greater the risk, especially if the radiation was administered during breast development.
What is interesting is that the more people are knowledgeable about issues related to screening the more they tend to decide against having mammography. This is an eye-opener from Gerd Gigerenzer's Gut Feelings:
"Do doctors take the tests they recommend to patients? I once gave a lecture to a group of sixty physicians, including representatives of physicians' organizations and health insurance companies. ...Another doctor asked her [a gynecologist] whether she herself participates in mammography screening? 'No,' she said. 'I don't.' The organizer then asked all sixty physicians the same question (for men: 'If you were a woman, would you participate?'). The result was an eye-opener: not a single female doctor in this group participated in screening, and no male physician said he would do so if he were a woman."
Do Breast Screening Invitations Give All the Facts?
Several research studies have been carried out analyzing the letters and accompanying documentation sent to invite women to attend breast screening programmes, as well as other literature and websites.
Regarding the latter, a study found that all the websites of advocacy groups, such as cancer charities, and of governmental institutions from Australia, Canada, Denmark, New Zealand, Norway, Sweden, the United Kingdom and the United States (all countries with breast screening programmes) analysed in the study recommended mammographic screening, but did not adequately inform about the major harms of screening, overdiagnosis and overtreatment, and the information they chose to give was often misleading, erroneous and did not reflect recent findings.
In contrast, all the sites of consumer organisations questioned breast screening. They all covered overdiagnosis and overtreatment. The information they gave reflected recent findings, and these sites were much more balanced and comprehensive.
The study concluded that the information provided by the websites of professional advocacy groups and governmental organisations is poor and severely biased in favour of participation in screening. Few websites, it said, live up to accepted standards for informed consent such as those stated in the General Medical Council's guidelines.
Regarding the invitation material, a study examining mammography invitations in Australia, Canada, Denmark, New Zealand, Norway, Sweden and the United Kingdom - all countries with publicly-funded breast screening programmes - have found that the major harms of screening, overdiagnosis and subsequent overtreatment of healthy women, was not mentioned in any of 31 invitations examined. It also found that 10 invitations claimed that screening leads to either less invasive surgery or simpler treatment, whereas in fact it results in 30% more surgery, 20% more mastectomies, and more use of radiotherapy due to overdiagnosis; and that only 15 invitations mentioned pain caused by mammography.
The study pointed out the conflict of interest occurring when the people responsible for the success of the screening programme are also those who provide the information about it, because the first group will desire high participation rates but at the same time full and correct information about potential harms may discourage participation.
Following the publication of that research in the British Medical Journal, the breast screening information leaflet used in the UK was changed, and subsequenly analized again by the same team of researchers at the Nordic Cochrane Centre.
The results were similar to the first study. The conclusion was that little had changed. An alternative, evidence-based leaflet was suggested at the end of this research, giving information which we have partly used to compile our box of trial results above.
In the UK, the NHS (National Health Service) documentation mentions false positives, but it does not tell you how common false positives are: according to recent systematic reviews of the data, more than 1 in 10 women attending breast screening for 10 years will receive at least one false positive, but according to other reviews, the corresponding figure for women undergoing 10 regular annual or biennial mammograms is 1 in 2 women. The younger the woman, the higher the percentage of false positives.
What To Do?
They are "overselling" breast screening, considering how little is still known about breast cancer, with consequences for its diagnosis, prognosis and treatment. A screning programme is only good insofar as the diagnosis and prognosis are clear and a tretament that at least stops the progression of cancer, even if it doesn't cure it altogether, is available. Breast cancer is still a very unknown disease in many respects.
On one side you have the story about a woman whose life she says was saved by breast screening, on the other there is the interview with a woman whose life was made hell by the discovery of a possibly benign DCIS, and the article about a third person who went through a nightmare of false positives believing that she has breast cancer when she hasn't.
What is the truth? All these stories are part of the truth, which is why making a choice on this issue, which faces all women aged 50 and over in developed countries with a mass breast screening program, especially when it's free as in Britain, is so difficult. The ultimate decision rests with the woman: will you be the one in 2,000 who will be saved by a mammogram (although it's difficult to tell, even a posteriori, because there is always the possibility that the breast cancer discovered in you, particularly if it was a DCIS, would never have developed into a malign tumor, or will you be the woman who has to suffer all the damaging physical and psychological consequences of false positive diagnoses, or will you simply have done something that puts your mind at rest with just a little discomfort and anxiety of going through the test, or will you be the person with a detected DCIS which was benign but nobody could tell so you had to be treated as a cancer patient, with all that involves?
There are more questions than answers.
The best way to make a good, informed choice is to be provided with all the known facts and data: that is at least fair. But unfortunately in this case, although being fully informed is a necessary prerequisite, it is still not sufficient to be able to make a fully satisfactory and rational choice, due to all the uncertainties involved.
Should you attend breast screening? And remember that after that decision you could face another: if they find DCIS (Ductal Carcinoma In Situ), which according to the best estimates happens in 1 out if 200 cases, will you accept treatment, invasive and with serious side effects, or not, knowing that more likely than not it will not progress but it might?
There is, anyway, no single way to assess the benefits versus risks balance. Each woman has to take into account her personal risk factors for breast cancer, as outlined above, and the importance she gives to all the other possible outcomes and variables described here.
I am a woman of 57 living in the UK, and my choice is that I will not attend breast screening unless the current circumstances, due to technological or clinical advances, change.
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