What is the risk-benefit ratio of the cancers picked up by mammograms and the cancers caused by mammograms?
Over the last few decades, our radiation exposure has nearly doubled, due almost exclusively to medical sources, such as CT scans. While we’ve known that higher dose radiation from CT scans and angiograms, for example, can cause breaks in our DNA, we now know that mammograms can, too. As you can see at 0:29 in my video Can Mammogram Radiation Cause Breast Cancer?, you can find x-ray–induced DNA damage in white blood cells drawn from women right after mammograms. When you consider that the “female breast has a considerably lower blood volume” in the first place, which is then squeezed out during the procedure before it mixes with the unexposed blood from the rest of the body, it’s amazing that DNA damage circulating throughout their system can still be picked up. So, what they found “underestimates” the DNA damage in the breast tissue itself.
But doctors tell women “there is nothing to worry about” and there are only a few extra cases of breast cancer caused by mammograms. What? Mammograms causing breast cancer? Yes. The risk of radiation-induced breast cancer from modern, low dose, digital mammograms depends on how often you get screened and at what age you start, as you can see at 1:13 in my video. For a group of 100,000 women screened annually from age 40 to 55 years and then every other year until age 74, “it is predicted that there will be 86 cancers induced and 11 deaths due to radiation-induced breast cancer”—meaning researchers estimate 11 of those women will die from breast cancer they never would have gotten had they not decided to get mammograms and expose themselves to that radiation. They even calculated the lifetime risk of developing a radiation-induced breast cancer after just getting a single mammogram, as you can see at 1:47 in my video.
Women with large breasts may carry additional risk because their mammograms may require additional views. The greater radiation dose is expected to translate into a greater risk for radiation-induced breast cancer and breast cancer death, tripling the lifetime attributable risk of developing breast cancer because of the mammogram radiation exposure.
As well, the earlier one starts screening, the risk increases, since a cancer will have more time to grow. This comes up for women with BRCA gene mutations, for whom screening is sometimes recommended starting in their twenties. At that age, however, mammograms may cause as many breast cancer deaths as they prevent. A net benefit would be expected at 35 years of age, though, likely the same for women without BRCA mutations. “The risk of radiation-induced cancer from mammography is not negligible, however the potential for mortality benefit is generally considered to outweigh the risk of death from radiation-induced BC [breast cancer] attributed to mammography screening,” resulting in a benefit-to-risk ratio in lives of 10 or more to 1.
These estimates on how much breast cancer mammogram x-rays may cause “rely heavily on data from the atomic bomb survivors,” who were exposed more to gamma rays, which are like high-energy x-rays. But, it turns out the lower energy x-rays used in mammography are even worse—“approximately four times…more effective in causing mutational damage than higher energy X-rays. Since current radiation risk estimates are based on the effects of high energy gamma radiation, this implies that the risk of radiation-induced breast cancers for mammography X-rays are underestimated by the same factor,” that is, about four times worse than previously estimated. Even if that were true, though, the benefit-to-risk ratio would still favor mammograms, which is why you can read editorials in radiology journals asserting that “concern about radiation exposure should not prevent women from undergoing life-saving mammography screening.”
In actuality, “no trial has ever shown an overall mortality benefit from screening mammography. Thus, if there is a detrimental effect of radiation exposure from mammography, even a small effect could offset any benefit of mammography.”
KEY TAKEAWAYS
- As with CT scans and angiograms, the higher dose radiation from mammograms can cause x-ray-induced DNA damage.
- There is a risk of radiation-induced breast cancer from modern, low dose, digital mammograms, depending on how frequently screening is conducted and at what age it starts.
- Out of 100,000 women screened annually from 40 to 55 years of age and then every other year until she is 74, researchers predict 86 cancers will be induced and 11 deaths caused by radiation-induced breast cancer.
- Women with larger breasts may be at additional risk as their mammograms may require additional views and, therefore, greater radiation exposure.
- The estimates of x-ray-induced breast cancer from mammograms rely on data from atomic bomb survivors who had been exposed to gamma rays, which are like high-energy x-rays. In fact, the lower energy x-rays used in mammography are worse than gamma rays—about four times more effective than higher energy x-rays in causing mutational damage.
- No scientific trial has ever shown an overall mortality benefit from mammogram screening.
For more on radiation exposure from other sources, see:
What about cell phones? See:
The greatest radiation risk from mammograms is the exposure to radiation treatments for overdiagnosed pseudo disease. I explore that more in Understanding the Mammogram Paradox, which, like this, is part of my 14-part series on mammograms.
There is just so much confusion when it comes to mammography, combined with the corrupting commercial interests of a billion-dollar industry. As with any important health decision, everyone should be fully informed of the risks and benefits, and make up their own mind about their own bodies. See the other videos in my 14-part series for more:
For more on breast cancer, see my videos Oxidized Cholesterol 27HC May Explain Three Breast Cancer Mysteries, Eggs and Breast Cancer and Flashback Friday: Can Flaxseeds Help Prevent Breast Cancer?.
I was able to cover colon cancer screening in just one video. If you missed it, see Should We All Get Colonoscopies Starting at Age 50?.
Also on the topic of medical screenings, check out Flashback Friday: Worth Getting an Annual Health Check-Up and Physical Exam?, Is It Worth Getting Annual Health Check-Ups? and Is It Worth Getting an Annual Physical Exam?.
In health,
Michael Greger, M.D.
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