The Low Down on Mammograms
Mammograms have been a hotly debated and controversial topic for a while and its no wonder that many women feel confused about what to do! My personal view is this:
– Our three-yearly mammograms as advocated on the NHS is a sensible approach because currently, we don’t have anything better (at present, there is no study which definitively proves that ultrasound screening alone lowers mortality rates for breast cancer, unlike the very modest benefits of mammography. Hence ultrasound by itself as an s screening tool for breast cancer isn’t recommended but could be useful as an adjunct eg to evaluate women with dense breasts.
– Mammograms have at best a modest effect on reducing breast cancer and they do also pose a risk of overdiagnosis. The Cochrane Collaborative review published in 2013 states: “If screening reduces breast cancer mortality by 15% and overdiagnosis and overtreatment is at 30%, it means that for every 2000 women invited for screening throughout 10 years, one will avoid dying of breast cancer and 10 healthy women, who would not have been diagnosed if there had not been screening, will be treated unnecessarily.”
– If a lesion is found on mammography it is worth considering further evaluation with the combination of ultrasound and magnetic resonance imaging to assist diagnostic and treatment decisions. Ultrasound is also very useful in ‘guiding the needle‘ during a followup biopsy.
-Mammograms are less effective for women with dense breasts – women who have been shown to have dense breasts on mammogram should definitely go on to have an ultrasound to exclude a cancer
– Women carrying the BRCA1/2 gene should have non-ionizing radiation imaging techniques (such as magnetic resonance imaging) as the main tool for surveillance. This is because women with the BRCA1/2 gene are particularly vulnerable to radiation-induced cancer and women carrying this mutation who were exposed to diagnostic radiation before the age of 30 were twice as likely to develop breast cancer, compared to those who did not have the mutated gene.
– There is no evidence that countries using the British/European model of 3 yearly screening have any higher rates of breast cancer mortality than countries that employ more frequent screening which is a great reason not to have to undergo them more frequently.
More on the following points below…..
Mammograms save lives but the benefits are modest – in reality, they may be preventing only 1 death per 1000 women screened
In 2012, an analysis of 3 decades of screening mammography and breast cancer incidence concluded that yes, there were substantial increases in the number of cases of early-stage breast cancers detected through screening mammography, but that screening mammography has only marginally reduced the rate at which women present with advanced cancer. They concluded that the imbalance suggests that there is substantial overdiagnosis, accounting for nearly a third of all newly diagnosed breast cancers. Screening is having, at best, only a small effect on the rate of death from breast cancer.
In another 2011 publication of Swedish data based on 3 decades of follow-up, major benefits of screening were observed, with a 31% lowered risk of breast cancer mortality in the screening group. However, the number of women needed to screen for 7 years to prevent 1 breast cancer death was 414.
What about the radiation?
This is not really a worry for most women having 3 yearly screening from the age of 50 since the amount of radiation that you get from a screening mammogram is almost the same as the amount you would receive over 3 months from your usual surroundings (e.g. sun, rocks, soil, buildings, air and food) and the risk of new cancer starting due to mammography radiation is far lower than the number of lives saved by mammography. However, if a woman had a BRCA1/2 gene mutation, the radiation from annual mammograms from the age of 25 would be a worry in my opinion.
What about the risk of false positives?
According to a recent review in JAMA Internal Medicine, if 1,000 US women aged 50 years are screened annually for a decade, 0.3 to 3.2 will avoid a breast cancer death and 490 to 670 will have at least 1 false alarm.
In the same JAMA review, it was found that 3 to 14 women will be over-diagnosed and be treated [i] for cancers that would actually have never caused death. Maybe the rate of over-diagnosis is probably somewhere around 10%-20% but even this we don’t know! We currently have no way of knowing if a small tumour will grow or potentially remain small and the bottom line is that we CANNOT predict who has a non-lethal vs. lethal breast cancer.
However, rather than get overanxious at an abnormal mammogram result, we should be aware of the high rate of false alarms and go on to further evaluate the lesion with ultrasound and MRI.
Treating breast cancer as early as possible is the best way to improve survival, and seeing women later in the process, with later-stage breast cancers, may require more extensive surgical treatment and more extensive chemotherapy than would have been otherwise needed.
So what’s a woman to do?
Every woman must be informed of the benefits (modest) and risks (mainly of overdiagnosis – therefore a recall should not cause panic, and further evaluation with US or MRI is sensible) and then she is in a position to do what feels right for her, based on her individual risk factors.
Known risk factors for breast cancer include obesity, more than 7 alcohol drinks per week and a first-degree relative with a breast cancer history.
[i] Welch G, Passow H. Quantifying the benefits and harms of screening mammography. JAMA Internal Medicine; online Dec 30, 2013.
[ii] Cochrane Database Syst Rev 2013;6:CD001877
[iii] Welch G. Screening Mammography- A long run for a short slide. NEJM 2010;Sept 23: 1276-1278
[v] Miller A, et al. Twenty five year follow-up for breast cancer incidence and mortality of the Canadian National Breast Screening Study: randomised screening trial. BMJ 2014;Feb 11:348:g366
[vi] Kalager M, Zelen M, Langmark F, Adami H. Effect of screening mammography on breast cancer mortality in Norway. NEJM 2010; 363: 1203-1210.
[vii] Mandelblatt J, Cronin K, Bailey S, et al. Effects of mammography screening under different screening schedules: model estimates of potential benefits and harms. Ann Intern Med 2009; 151:738-47.
[viii] Autier P, et al. Breast cancer mortality in neighbouring European countries with different levels of screening but similar access to treatment: Trend analysis of WHO mortality database. BMJ 2011 July 28;343:d4411.
[ix] Bleyer A, Welch G. Effect of three decades of screening mammography on breast-cancer incidence. NEJM 2012;267(21):1998-2005.
[x] Tabar L, et al. Swedish Two-County Trial: Impact of mammographic screening on breast cancer mortality during 3 decades. Radiology 2011 Sep; 260:658.
[xi] P. Autier, A. Koechlin, M. Smans, L. Vatten, and M. Boniol. Mammography Screening and Breast Cancer Mortality in Sweden. J Natl Cancer Inst, 2012,July 17