The mammogram paradox is that women who are harmed the most, are the ones who claim the greatest benefit.

While false-positive results, pain during the procedure, and radiation exposure may be among the most frequent harms associated with mammogram screening, overdiagnosis “is now recognized as the most serious downside of population breast screening.” Overdiagnosis is so serious that the question has been raised whether it makes breast screening “worthless.” Indeed, the value of performing routine mammograms at all is being questioned due to overdiagnosis, which is “the diagnosis and treatment of breast cancer that would never have become a threat to a woman’s health, or even apparent, during her lifetime.”

“The public thinks once you have a cancer cell in your body, it will progress predictably and inevitably to a terrible death. That is simply not true of most cancers.” Some cancers outgrow their blood supply and become starved and wither away, and others are recognized by our immune system and successfully contained. Others still “are simply not that aggressive in the first place,” so, although they might continue to grow unchecked, it may be at such a slow rate that it would be decades or even centuries before they could be big enough to cause any problems. So, in effect, you would die with your tumor instead of from your tumor.

Indeed, autopsy studies of young and middle-aged women who died in a car accident, for example, found that 20 percent of them had cancer in their breast. That’s about one in five women walking around with breast cancer. Now, that sounds a lot scarier than it is because, in that age range, the risk of dying from breast cancer is less than 1 percent. In fact, your risk of ever dying from breast cancer in your lifetime is less than 4 percent, which goes to show that many of these cancers that are found incidentally—most of them, in fact—would likely have fizzled out on their own. 

The problem is that we continue to have an antiquated definition of cancer that dates back to the 1860s. To this day, cancer is defined by what it looks like under a microscope, not by what its subsequent behavior is. So, according to that mid-19th century definition, one in five women followed in that one study technically had cancer, but that doesn’t necessarily mean the cancer would go on to do anything. 

So, if cancer is so common, do you even want to know about it? This is the question I discuss in my video Understanding the Mammogram Paradox. Certainly, if the cancer will progress and cause a problem, then catching it early could save your life, but if it’s never going to grow, if it’s going to remain microscopic, then finding it could actually hurt you. A likely scenario upon finding it could be: We found that you have cancer so we have to treat it with surgery, chemotherapy, and radiation—whatever it takes—and then you’d suffer all the physical effects of treatment and the psychological hell of fearing for your life. But, if in fact the cancer was never going to cause a problem, all of that would have been completely unnecessary. That is overdiagnosis.

These kinds of car accident-type autopsy studies, as you can see at 2:55 in my video, show that 7 to 39 percent of women aged 40 to 70 are walking around with tiny breast cancers and 30 to 70 percent of men older than 60 have prostate cancers. And, up to 100 percent of older adults have microscopic cancers in their thyroid glands, yet only 1 in a 1,000—0.1 percent—ends up suffering or dying from thyroid cancer. Normally, the cancer just sits there and doesn’t do anything. Likewise, even though the majority of older men may have tiny cancers in their prostates or a significant number of women have them in their breasts, the lifetime risk of death or cancer spread is only about 4 percent. So, if you had a magic wand that could pick up cancer with 100 percent accuracy and waved it in front of people, your overdiagnosis rate—the probability that the prostate cancer you’d pick up would have turned out to be harmless—is about 90 percent. This is also the case for nearly every single thyroid cancer and a significant proportion of breast cancer cases. This is why screening for these cancers—cancer of the prostate, thyroid, and breast—can be tricky or even potentially dangerous. In many cases and sometimes most cases, you would have been better off if they had never found the cancers. 

This is not true for all cancers, though. Researchers have found “little evidence of overdiagnosis of either cervical or colorectal cancer,” for example. Those cancers seem to continue to grow, so the earlier you catch them, the better. When pap smears were instituted, cervical cancer death rates plummeted, for instance, and just a single sigmoidoscopy performed between the ages of 55 and 65 may decrease one’s risk of dying from colorectal cancer by up to 40 percent. In contrast, a study found that “annual mammography in women aged 40-59 does not reduce mortality from breast cancer” at all. But, if we assume a 15 percent drop and a 30 percent overdiagnosis rate, which most studies have found, that would “mean that for every 2000 women invited for [mammogram] screening throughout 10 years, 1 woman will have her life prolonged and 10 healthy women, who would not have breast cancer diagnosed if there had not been screening, will be treated unnecessarily.” That is, ten healthy women would be overdiagnosed. If they had skipped screening, they would not have been told they have breast cancer and undergone treatment they didn’t need. 

“Furthermore, about 1000 women…will have had a false-positive diagnosis,” a false alarm that can be stressful while you wait for the results. But the harms caused by becoming a cancer patient unnecessarily can be lifelong—and can even mean a shorter life. “It is also important to be aware that some of the healthy overdiagnosed women will die from their treatment.” For example, radiation treatments for breast cancer can’t help but penetrate down into the heart as well, increasing the risk of heart disease, which is the number one killer of women. 

This raises questions about doing routine mammography screening at all, as it “converts thousands of healthy women into cancer patients unnecessarily”—and some may not make it out alive. Ironically, though, those who do survive become mammography’s biggest cheerleaders, thinking mammograms saved their lives. The mammogram found a cancer they didn’t even know they had. Yes, the treatment was rough with the surgery, radiation, and chemo drugs, but it worked and life was saved. “What a relief she got that mammogram!” “You should get one, too!” In actuality, the more likely scenario—in fact, maybe the ten times more likely scenario—is that the treatment didn’t do anything because the cancer wouldn’t have hurt you anyway. So, you went through all that pain and suffering for nothing. That’s the crazy thing about mammograms: the people who are harmed the most are the ones who claim the greatest benefit.


The mammogram paradox: Women who are harmed the most are the ones who claim the greatest benefit.
Overdiagnosis—the diagnosis and treatment of breast cancer that never would have even threatened the woman’s health—is recognized as the most serious downside of population breast screening, even more than false-positives, pain during the procedure, and radiation exposure.
It is a myth that a cancer cell will necessarily progress and result in death. Some cancers wither away on their own, others are successfully contained by our immune system, and many may grow so slowly that it may be decades before they could be problematic.
Cancer, when found, may be treated with surgery, chemotherapy, and radiation, causing physical and psychological trauma. If that cancer was never going to cause any health problems, none of that would have been necessary.
For example, 7 to 39 percent of women aged 40 to 70 have tiny breast cancers, 30 to 70 percent of men older than 60 have prostate cancers, and up to 100 percent of older adults have microscopic cancers in their thyroid glands, yet only 0.1 percent ends up suffering or dying from thyroid cancer.
Because of overdiagnosis, screening for cancers of the prostate, thyroid, and breast can be tricky or even potentially dangerous, but researchers have found little evidence of overdiagnosis of colorectal or cervical cancer, so early identification is best.
Routine mammograms have been said to unnecessarily convert thousands of healthy women into cancer patients. Ironically, those who survive often credit mammography for saving their lives by first identifying cancer—even though it may be ten times more likely the cancer wouldn’t have ended up causing any problems. But, because of overdiagnosis, she may have undergone surgery, radiation, and chemo anyway.

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. This is the eighth in my 14-part series on mammograms, which includes:

Nine Out of Ten Women Misinformed About Mammograms
Mammogram Recommendations: Why the Conflicting Guidelines?
Flashback Friday: Should Women Get Mammograms Starting at Age 40?
Consequences of False-Positive Mammogram Results
Do Mammograms Hurt?
Can Mammogram Radiation Cause Breast Cancer?
Understanding the Mammogram Paradox
Overtreatment of Stage 0 Breast Cancer DCIS
Women Deserve to Know the Truth About Mammograms
Breast Cancer and the Five-Year Survival Rate Myth
Why Mammograms Don’t Appear to Save Lives
Why Patients Aren’t Informed About Mammograms
The Pros and Cons of Mammograms

For more on breast cancer, see my videos Oxidized Cholesterol 27HC May Explain Three Breast Cancer MysteriesEggs and Breast Cancerand Flashback Friday: Can Flax Seeds 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.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations:

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2013: More Than an Apple a Day

2012: Uprooting the Leading Causes of Death