How safe are mammograms?
Updated: Jun 14, 2021
Lately I have put off getting a mammogram, mainly because I worry about the negative effect that could result from the radiation. But how bad is the radiation from a mammogram really and is it worth the risk? What alternatives are there?
I started getting mammograms in my early 40's - every second year. If you've ever had one, you will know that they are not exactly pleasant. But if they can detect breast cancer, I figured it's worth it. Then, a few years ago, I started hearing about the negative effects mammograms can have and consequently haven't had another one since. The more I learnt, the more I asked myself why I would look for breast cancer with a test that can actually be the cause of breast cancer?
Mammograms - to have or not to have
On one hand you have doctors and the breast cancer foundations encouraging regular mammograms, on the other hand you have experts warning about the long term exposure risks to radiation and the high percentage of false positiives that lead to treatment without being necessary. Who should we believe? I did some research and here are the pros and cons I could find:
A Swedish study published in the journal Radiology in 2011 was the longest ever trial of mammograms for breast cancer detection. It was also the first to track the effects of this screening method alone on breast cancer mortality. After following more than 133,000 women, ages 40 to 74, over a period of nearly 30 years, the researchers found that women who had a mammogram were 30 percent less likely to die from breast cancer compared to women who didn't have mammograms. For every 414 women screened with a mammogram over a seven-year period, one breast cancer death was prevented.
A 2010 Norwegian study, which was led by researchers at the Harvard School of Public Health, also found a lifesaving benefit from mammograms—although it wasn't as significant. The researchers looked at data from about 40,000 women who took part in the Norwegian breast cancer screening program. The study found that mammogram screening only reduced the rate of breast cancer death by about 10 percent in women ages 50 to 69. The reduction was less—8 percent—in women over age 70. Yet a follow-up to the study noted that six to 10 out of every 2,500 women screened were "overdiagnosed," meaning tumors were found and treated that were never likely to become life threatening.
A newer breast cancer screening technology - tomosynthesis - supposedly creates more detailed 3D images of the breast tissue than the standard 2D mammogram. Some researchers say it can help detect the disease earlier than a conventional mammogram. Other health experts say that they don't have better success rates than the standard mammogram. The radiation dose is similar to that of a normal mammogram.
On average the total radiation dose for a standard 2D mammogram with 2 views of each breast is anywhere between 0.44 - 1 millisieverts, or mSv. (mSv is a measure of radiation dose). The amount of radiation needed also depends on breast density and on breast size. Furthermore, dose levels are known to vary between clinics and systems used. An example is a study done by Wallis, where patients were examined both in England and in Sweden, with an average breast dose per DBT scan (digital breast tomosynthesis) that was about 17% higher in England than in Sweden (avg. 0.82 mGy and 0.70 mGy, respectively). For the patients examined with a normal mammogram, the resulting average breast dose was 50% higher in England than in Sweden (avg. 1.2 and 0.6 mGy, respectively). The DBT units in England and Sweden were the same, while the normal mammogram units were from different manufacturers (GE and Sectra), which contributed to the dose discrepancy. This goes to show, that you can't be sure if you will get a lower dose of 0.44 mSv or a dose of 1.2 mSv or higher.
To put the dose into perspective, the worldwide exposure to background radiation (that's radiation that occurs in the environment - in the air, in our food and water etc.) is on average about 2.4 mSv per year. The dose of radiation used for a screening mammogram of both breasts is about the same amount of radiation a woman would get from her natural surroundings between 2 to 6 months. Should you be called back for another mammogram after some irregularities are found, the radiation dose gets even higher.
An article in the US National Library of Medicine says that for a cohort of 100 000 women each receiving a dose of 3.7 mGy to both breasts and who were screened annually from age 40 to 55 years and biennially thereafter to age 74 years, it is predicted that there will be 86 cancers induced and 11 deaths due to radiation-induced breast cancer.
The American Cancer Society alleges that in recent years the average amount of radiation a person is exposed to from medical tests has risen. The increased risk of cancer from exposure to any single test is likely to be very small. But radiation exposure from all sources can add up over one’s lifetime, so imaging tests that use radiation should only be done if there is a good medical reason to do so. The usefulness of the test must always be balanced against the possible risks from exposure to the radiation. In some cases, other imaging tests that don’t use radiation such as ultrasound or MRI may be an option. But if there is a reason to believe that an x-ray or CT scan is the best way to look for cancer or other diseases, the patient will most likely be helped more than the small dose of radiation can hurt.
There is quite a bit of disagreement between cancer experts as to how often you should have mammograms and what age you should start. The American Cancer Society recommends yearly mammograms starting at age 45. However, the US Preventive Services Task Force recommends mammograms only for women aged 50 - 74 and only every 2nd year.
In New Zealand, the Breast Cancer Foundation suggests to have yearly mammograms for women between the ages of 40 - 50. Between 50 - 69 they recommend mammograms every second year, as cancers usually grow slower when you get older. In New Zealand women between the ages of 45 - 69 are able to get free mammograms every 2 years through BreastScreen Aotearoa.
In most European countries, women are still advised to have mammograms every 2 years between the ages of 50 - 69 (see graph below). In Switzerland, the Swiss Medical Board has caused an uproar with their recommendation to abolish the regular screening due to the potential harm.
What are the alternatives?
Self examination: A breast self-exam is a screening technique you can do at home to check for breast lumps. The best time to do a breast self-exam is a few days after your monthly menstrual cycle ends. Hormonal changes can affect the size and feel of your breasts, so it is best to perform the exam when your breasts are in their normal state. Women who do not menstruate should choose a certain day to perform the exam, such as the first of each month. Don't panic if you find a breast lump - most breast lumps are noncancerous. Any time you feel an abnormality in your breast, see your doctor.
Ultrasound: It does not use radiation, but uses high frequency sound waves to produce an image of the breast. It is pain free and harmless. It's not normally used as a routine breast cancer screening, but often after a mammogram detected an abnormality. A 2015 study in the Journal of National Cancer Institure showed that the detection rate with ultrasound is similar to that of a mammogram. The downside is that there are more false positives.
Thermography: This is a non-invasive, no-contact digital infrared thermal imaging. No radiation is used. It's harmless and pain free. It uses infrared sensors to detect heat and increased vascularity (angiogenesis) as the byproduct of biochemical reactions. The heat is compiled into an image for computerized analysis. It detects physiological changes, but cannot pinpoint the exact area of suspicion inside the breast and cannot diagnose cancer. The Breast Cancer Foundation NZ as well as the FDA does not support Thermography, stating a lack of evidence for efficiency.
MRI: MRI (magnetic resonance imaging) of the breast uses a powerful magnet, radio waves and a computer to produce detailed images of the breast. An injection of a contrast medium (Gadolinium) is often used to assist detection. MRI is mostly used as a supplementary tool in breast cancer detection, after mammography and ultrasound. It is often used to evaluate the extent of disease and is the best method of determining whether silicone implants have ruptured. It may be recommended in addition to mammography for screening women who are at high risk of breast cancer due to family history or known gene mutation, but is not generally used in regular breast screening. MRI is a costly procedure which takes more time to perform than other imaging methods and requires specially trained radiologists to review the images.
Mammograms can pick up early breast cancers, but aren't guaranteed to save your life. Screening can miss up to 20 percent of tumors, especially if you have very dense breasts. Or they can detect a cancer that isn't there, potentially sending you for an ultrasound or biopsy when you don't need it. And finally, mammograms expose you to radiation, that could cause you breast cancer.
None of the alternative methods by themselves are hundred percent accurate either.
Whatever you decide to do is a personal choice - every woman needs to make an informed decision for herself. I personally think that living a healthy lifestyle is your best bet for beating any type of cancer.
Harvard Health Publishing: https://www.health.harvard.edu/womens-health/do-you-need-mammograms
Breast Cancer Foundation New Zealand: https://www.breastcancerfoundation.org.nz/
European Society of Breast Imaging: Mammography: an update of the EUSOBI recommendations on information for women
New England Journal of Medicine: http://www.nejm.org/doi/full/10.1056/NEJMp1401875
Swiss Medical Board:http://www.medical-board.ch/fileadmin/docs/public/mb/fachberichte/2013-12-15_bericht_mammographie_final_kurzfassung_e.pdf
MJ Yaffe, JG Mainprice: Risk of radiation-induced breast cancer from mammographic screening https://www.ncbi.nlm.nih.gov/pubmed/21081671/
American Cancer Society: https://www.cancer.org/cancer/cancer-causes/radiation-exposure/x-rays-gamma-rays/do-xrays-and-gamma-rays-cause-cancer.html
RSNA Radiology: http://pubs.rsna.org/doi/full/10.1148/radiol.10100570
Wallis MG: Two-View and Single-View Tomosynthesis versus Full-Field Digital Mammography: High-Resolution X-Ray Imaging Observer study http://pubs.rsna.org/doi/10.1148/radiol.11103514?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dpubmed
T.M. Svhan, N. Houssami, I. Sechopoulos, S, Mattsson: Review of radiation dose estimates in digital breast tomosynthesis relative to those in two-view full-field digital mammography https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5064843/#R19
Dr. Mercola: https://articles.mercola.com/sites/articles/archive/2016/10/25/mammogram-effects-risks.aspx
Breast cancer mammograms: overrated – and over-diagnosing women: https://www.theguardian.com/commentisfree/2014/apr/28/breast-cancer-mammograms-early-detection-research
Breast self examination: https://www.maurerfoundation.org/about-breast-cancer-breast-health/how-to-do-a-bse-breast-self-exam/