Do Mammograms Cause Cancer?

Let’s just start with some facts on the magnitude of the risk of female breast cancer (National Cancer Institute SEER statistics, 2012):
1.  In the US today, about 2.7 million women have had a history of breast cancer.  That’s about the population of the city of Chicago, the third most populous city in the US.
2.  Over 12% of women born today will be diagnosed with breast cancer during their lifetime.  That’s about 1 in 8.
3.  The incidence rate (new cases) is 124.3 per 100,000 women per year.
4.  The median age at diagnosis is 61 and the median age at death is 68.
5.  If breast cancer is caught while it is still local; before it spreads, the 5 year relative survival is 98.6%.  Once it has metastasized, the 5 year relative survival drops to 23.8%.
6.  Breast cancer is the second leading cause of cancer death in women, behind lung cancer.

It is in 4 and 5 that the importance of screening is highlighted.  We need a way to diagnose cancer early on, while it is still easier to treat and offers a very positive prognosis.

Enter the breast cancer screening and diagnostic tests.  Let’s be clear about the difference between those two:

A.  Breast cancer screening is conducted on someone without signs or symptoms of disease.  It typically identifies risk categories and gives a healthcare professional additional information needed to guide further testing, but it doesn’t stand on its own as a result.  This might include a medical history, a BRCA/genetic screening panel, breast exam, X-ray mammography or other imaging technology.

B.  Breast cancer diagnostic tests are conducted when a risk is identified.  These are usually the higher risk tests, but they can more definitively identify the important information about the disease.  In the case of breast cancer, this may involve biopsy, diagnostic imaging or other tests.

Mammograms are a very common screening method, but are recently somewhat controversial.  Let’s take a quick look at what the recent research on the topic has uncovered:

1.  Mammograms CAN increase cancer risk, but they prevent far more cancer than they cause.

A woman is exposed to about 4 milliGrays (mGys) in a mammogram screening.  For comparison, an abdominal CT scan might expose you to about 8 mGys.  It’s not inconsequential.  It can cause DNA damage that can lead to cancer, but so can flying in an airplane or living in an area with abundant radon gas.  We need a better way of evaluating the actual risk than simply: “Radiation bad, no-radiation good”.  This is precisely what studies have attempted to evaluate.

If we limit the biennual mammogram risk/benefit calculation to women aged 40-49, a 1997 study found that for every life lost as the result of screening, about 50 were saved (J Natl Cancer Inst Monogr. 1997;(22):119-24.).  To put it another way, for every YEAR of life lost, 121 years were saved.  Given those odds, you are much, much more likely to be saved by screening than harmed.  However, you do have a right to know that the procedure does come with risks as well.

In the women aged 50-69 years category, the ratios of lives lost to lives saved may be much, much higher.  One study reports a ratio of 1 life lost for every 242 saved (J Med Screen. 1998;5(2):81-7.).


2.  Mammograms have a relatively high rate of false positives.

False positives, just to clarify, are when a test falsely indicates cancer exists where none actually does.  “Abnormal” mammography results only indicate cancer 1 out of every 10 diagnoses.  For some women, that means a lot of psychological distress and “needless” biopsies on tissue that later turns out to be benign.

3.  Mammograms have a low rate of false negatives, but they still won’t pick up all breast cancer.

The false negative is when the mammogram is read as “normal” missing the presence of breast cancer.  A mammogram fails to detect the presence of cancer in between 10 and 25% of cases where breast cancer can be confirmed later.  The large range is because of the difference in various studies on the topic.

Some studies suggest that mammograms are most effective when combined with a clinical breast exam.

4.  Although there are alternatives to X-ray mammograms, they aren’t going to replace mammograms anytime soon.

You may have heard about MRI breast cancer screening, or thermography (imaging the heat of your body), or Breast Pap smears, or some other similar tests.  If you haven’t, here’s a plain language “About.com” site that talks more about them.  The trouble is that none of them, alone, are as suitable for the primary mission of low-cost breast screening in small communities.  MRI’s, for example, give very good high definition imaging of breast tissue without the ionizing radiation exposure of an X-ray.  Unfortunately, they cost about 10 times as much, require the use of injected contrast agent, take an hour or more per scan, and are only available in certain geographies.  There are also certain types of breast cancer that an MRI has trouble identifying.  In many ways, the MRI is just TOO sensitive, and it requires a radiologist’s expertise to determine whether density differences are normal or abnormal.

The one other screening technique that should be included here is clinical breast exams, where a trained physician or nurse conducts a physical exam of the breast, feeling for any abnormalities in shape or texture.  It’s been shown to be very effective when done properly to detect large tissue abnormalities, but not very small growths.  It’s lower risk, can be low cost and easy to administer, and provides some additional value when used in conjunction with other techniques.

So all these techniques are generally quite good at improving the performance of overall breast cancer screening, but none are poised to replace mammography as a primary method of screening.

Why do I need to talk about this?  Because it’s very popular right now to exploit these facts in a vacuum; to twist them all to mean something much more profound: that mammograms for breast cancer screening are a bad decision for all women in all cases.  This is simply a LIE.  The only controversies are about how often a mammogram should be performed and at what age it should become a regular practice.  As we saw, the benefit to risk ration is overwhelmingly positive, but it increases even more with age.  If you are a woman between 40 and 49, you really should ask your doctor if an annual or biennual (every two years) mammogram is a good idea.  At 50 or older, the answer is almost certainly going to be yes because the risk of NOT being screened is so high.  Certain women, those with inherited BRCA genetic mutations, and those who are young (<30) really need to discuss the risks with their physician or a specialist, as the risk of exposure to radiation might outweigh the potential benefit.

Over the years, I’ve published a few rules in my videos.  The very first, and the most important of these I call C0nc0rdance’s First Law:

NEVER TAKE HEALTH ADVICE FROM THE INTERNET.

It’s intentionally self-inclusive.  If you want accurate health information, please, please, please consult a trusted healthcare provider.  The Internet is a free-for-all, and the content is as likely to be wrong as right.  Make sure you put your life in the hands of someone with experience and training and certification in medicine, not in the hands of someone who believes the Reptiloids are working in the service of the Illuminati to create a New World Order for the Alien Greys (/if that’s what your physician believes, get a new physician/).

A "typical course" flow chart for screening and diagnosis. Note that mammograms and clinical exams are really just an entry point to a more involved process.

11 comments on “Do Mammograms Cause Cancer?

  1. “5. If breast cancer is caught while it is still local; before it spreads, the 5 year relative survival is 98.6%. Once it has metastasized, the 5 year relative survival drops to 23.8%.”

    Does the “still local” breast cancer always spread and metastasize? And how do you know if it will or will not?

    What is the survival rate of women who have “still local” breast cancer, when they have no medical treatment whatsoever?

    What is the survival rate of women who have “still local” breast cancer, when they have no medical treatment whatsoever, but improve their lifestyle, e.g. less stress, better diet, proper regular exercise and so on?

  2. Hello and thank you for all your hard work.
    What is the best way to request a video or to post questions? I’m sorry for posting these questions not related to this post but I did not find any other means of contact.

    I would like to know more about standard deviations (SD) in order to be able to more fully understand articles at pubmed for instance. I have watched some videos and read a little but I’m wondering if there is a..more..pedagogic approach to it?

    I would be very interested in a video about “palm oil” and the fact that it is being used in so many baby food/formulas.

    A lot of reference is being made to http://www.ncbi.nlm.nih.gov/pubmed/16582027 and other articles. I’d like to know exactly how statistically significant are the findings? I can’t understand why companies such as Nestle keep adding palm oil if there are multiple studies pointing to the fact that palm oil is bad for bone mineralization and so on? Could you please shine some light on the topic?

    Again. Thank you.

  3. This is generally a good post, but you completely ignore one thing: the usefulness of breast self-examination is controversial. It is now considered optional, because studies have shown that it is largely unknown as to what effect, if any, it has on survival rates for cancer, while generally increasing the burden on the medical system.
    Also besides screening shouldn’t the emphasis be on prevention? Maybe next you can do a post about how the birth control pills has been shown to raise the risk of breast cancer, so has hormone replacement therapy, alcohol consumption, lack of exercise, obesity etc.. and these increases are not marginal, but huge when it comes to a country with many people like the US. In fact probably a lot more lives could be saved by modifying risk factors than the mammography.

    • First, I think you didn’t actually mean “breast self exam” but perhaps “clinical mammography” in your first paragraph? Annual mammograms for younger women are still somewhat a matter of subjective risk/benefit ratio cutoff. Older women benefit from mammograms without question. Perhaps you can cite a few papers that demonstrate strong evidence to the contrary?

      To your second point, yes, prevention and lifestyle interventions should be a major part of the solution. If you can come up with an effective way to convince people to eat right, exercise, reduce stress, and otherwise eliminate risk factors, please contact me by private email. I’d like to start a business with you.

  4. I’ve heard it mentioned that mammograms, due to the compression, can cause damage and possibly cause a mass to fragment which can cause cancer to spread quicker. Have you come across any evidence for or against things like that or is this one of those purely fictional stories you can find on the internet?

    • Purely fictional and spread by alt-med sites.

      Here’s a simple reductio question for proponents of this myth: Have you ever squished your finger in a door and had the fingernails start growing out the knuckle? That’s because metastasis requires very specialized cellular events, not simple pressure.

    • It’s going to be a useful adjunct to mammography in specific cases where breast tissue is very dense, but the big downside is that it takes a lot longer, uses more radiation, and uses an injected dose of radioisotope. There will always be more risks when a syringe penetrates the skin: allergies, embolism, infection, nerve damage, etc.

      Expert Rev Anticancer Ther. 2009 Aug;9(8):1073-80.
      “Molecular breast imaging.”

      http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2748346/?tool=pubmed

      “Currently, the main disadvantages of MBI are the long imaging time (4 × 10-min images) and the radiation dose associated with the injection of the Tc-99m sestamibi. Studies using multicrystal detectors have typically employed 25–30 mCi of Tc-99m sestamibi. With the dual-head CZT technology, we have utilized a dose of 20 mCi Tc-99m sestamibi. While this dose is low compared with doses used in many nuclear medicine procedures, it is high relative to that delivered by a mammogram. The effective dose from 20 mCi Tc-99m sestamibi is approximately 6.5 mSv [33]. By comparison, a screening mammogram has an effective dose of 0.7–1.0 mSv”

      Beware of TED Talks. Some of them contain very biased information. I enjoy them as well, but I always check out the research afterwards. Sometimes you realize that you’ve just listened to someone outside the mainstream of their field.

  5. This is extraordinary. Thank you so much sir. My mother and I greatly appreciate the amount of kindness, humanity and detail you put into all your work.

    Best wishes.
    Spinynorman1982

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