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.

Cutting Edge Cancer Diagnosis: Circulating Tumor Cells

This year’s AACR annual meeting focused a great deal on the vindication of a very old idea:  “seed and soil” model of metastasis.  The idea that little seed cells from a tumor circulate through the body looking for fertile ground to implant into and grow a metastatic tumor.  It’s only very recently that the technology has existed to provide a mechanism to detect these circulating seed cells.  This knowledge has proven to be very important in predicting which patients will respond to different therapies.

This video is taken from the only FDA approved technology to detect these circulating tumor cells (CTCs).  For any of you interested in what I do for a living, this is the clinical outcome of some technologies that I worked on at the “research use only” non-clinical level.  Being able to tag cells with magnetic particles or beads and separate or enrich from that binding.

It’s five minutes long and includes a commercial in the middle, but I thought it was a cool “infographic” format.  Very CSI!

March of Progress in Cancer Treatment

I came across this today, and I thought it might give some people hope for the future.  The source is: Cancer Research UK, Survival Statistics for the most common cancers.

What really strikes me is the number of cancers where 5 year survival is over 50%.  Pancreatic, Lung and Esophagus cancer are still very deadly, though.

Now take a look at where we’ve come from since 1971:

You can see that many cancers have radically improved in 10 year survival.  There’s still much room for improvement, but I take a lot of comfort in the progress we’ve made and are continuing to make.

My postdoc was at a cancer research center that shared a building with a cancer treatment clinic.  Every day I’d walk past the waiting room and the chemo chairs and see someone’s mother, grandmother, father, brother, sister awaiting treatment.  It was great motivation to take my job seriously.  F–k Cancer, Support Cancer Research!