Screen time

Dear Doctor Ninja,

I’ve just turned 40 and one of the first things my one of my girlfriends asked me was, “Are you going to start getting annual mammograms now?” I told her that I’m sure I would get a mammogram just as soon as my doctor recommended it. However, I’ve recently read an article about the science of mammograms and now I’m feeling conflicted. There has been some science that says that mammograms can cause more harm than good. There hasn’t been any cancer among my direct relatives, but my husband and I went through a stressful experience when he was diagnosed with stage III cancer five years ago. The thought of missing a cancer diagnosis stresses me out! What should I do?


B. Oob

The main delivery of the message that mammograms can cause more harm than good, B.Oob, comes from the Cochrane Review. It is a systematic review that takes all of the available research on studies that looked at whether getting vs not getting mammograms were useful and combines them to come up with an umbrella conclusion. Keep in mind that the latest version of this is from 2013, and that there should be an update in the next couple of years.

It should be noted that this message only applies to women with an average-risk for breast cancer, and not for women who are classified as high-risk for breast cancer.

What does a “harm” mean anyways?

The harm that is defined by the authors of the review is essentially receiving a diagnosis of breast cancer when you do not, in fact, have breast cancer, which is also known as a false-positive.

The harms of a false-positive include:

  • The stress of knowing that you might have cancer if your mammogram test is either inconclusive or positive, while you undergo more testing, which may require surgery.

  • Getting surgery for breast cancer that turns out to be not-needed if you didn’t actually have cancer.

  • Getting radiation or chemotherapy for breast cancer that turns out to be not-needed if you didn’t actually have cancer.

Ok, so what does a “good” mean then?

The good that is defined by the authors of the review include:

  • Not dying from breast cancer

  • Not dying from from another cancer

  • Not dying from anything else

It’s less important to talk about the last two points, namely because mammograms don’t seem to prevent people from dying from cancers that aren’t breast cancer or from things like car accidents or heart attacks.

The percentage of women who did not die from breast cancer as a result of mammogram detection is estimated at 15%, so out of 2000 women over 10 years of screening, 1 woman would be expected to be saved from dying from breast cancer. That’s very underwhelming for “good”.

There’s awful lot of death there. However, note that “good” does not include:

  • Not needing a full mastectomy

  • Not needing chemotherapy or radiation therapy

  • Not having a higher stage of cancer (which indirectly affects treatment decisions)

  • Other bad things that where you don’t just die.

Screening in most cancers has to do with detection, but also early detection. The idea is that detecting a cancer when it is “small” and before it has spread anywhere, leads to better results, not only in terms of not dying, but also in terms of how complicated or risky treatments need to be. For instance, women who don’t need chemotherapy or radiation for their breast cancers have fewer complications after reconstruction. And while chemotherapy or radiation are not entirely dictated by how early a breast cancer is detected, there is _a_ part of that decision that is affected by stage.

Does early detection matter?

The authors of the review argue that early detection means less as treatments for higher stage (more severe) breast cancers improve. From this perspective, if we reached a point where all stages of breast cancer could be treated, including stage IV, metastatic breast cancer, then the need to screen would be much less important. But, this is also from the lens of preventing death, not necessarily other bad things that don’t involve just dropping dead.

No, no and no.

But let’s take this Cochrane Review on mammograms at face value. If mammograms DO result in more harm than good, then what?

There are other two Cochrane Reviews on breast cancer screening: one about doing breast self-inspections as well as doctors doing breast exams, and the other on using ultrasound with mammograms. Both conclude that neither are acceptable screening methods either, because they also result in “too many false positives”; and the only large scale trial on breast self-examination failed because too many people just stopped doing it. All three reviews on breast cancer screening, therefore, fall back on the, “more research should be done in the future” cliché. The issue is that people like you, young grasshopper B. Oob, are living now and need guidance now, and not in the future.

So if the answer that science seems to be giving us today is, “Not mammograms,” it’s not very helpful because there’s no, “Instead of mammograms, do this.” It’s like that friend who you’ve agreed to go to dinner with, who says, “No, not that one,” to every restaurant you pick without offering a restaurant that you could go to. What do you do with a friend like this?

You pick a restaurant and don’t ask them what they think.

And how do you pick a restaurant? You do some deep soul searching for what’s important to you.

Your choices today are:

  1. A mammogram every 2-3 years starting when you’re 40

  2. A mammogram every 2-3 years starting when you’re 50

  3. A mammogram every 2-3 years starting when you’re 60

  4. A periodic mammogram with longer than 2-3 years in between, starting at any of the ages above

  5. No mammograms unless something is “wrong”

The implications of a false-positive, as we talked about above, run from the stress of having to go through more tests, all the while being uncertain as to whether you have cancer or not, to potentially having surgery or treatment (radiation and/or chemotherapy) that turns out to be not-needed after the fact.

After 10 mammograms, the false-positive rate is somewhere between 20% and 60%, depending on which study you choose. The authors of the review, after considering all of these studies, estimated the false-positive rate to be closer to 30%. So for 2000 women over 10 years, about 10 of them will undergo cancer treatment that is not needed.

A mammogram every 3 years means it will take 30 years to reach 10 mammograms where the false-positive rate seems to get awkward.

There are also the “four mammogram” figures, which vary according to age group, where women who have had four mammograms have a 3.6% chance of a false positive in their 40’s, 2.8% chance in their 50’s and 2.1% chance in their 60’s. If taken every 3 years, it takes 12 years to get to four mammograms in total.

No one has studied whether mammograms are useful in women older than 70 yet, which is why most guidelines don’t have strong recommendations for women older than 70.

At some point in your life, you might stop caring about breast cancer; or at least, you might stop being interested in pursuing aggressive treatment for breast cancer. Coming to terms with our own mortality is an interesting and potentially freeing exercise to take on, but beyond where this question probably goes. When might that might happen depends at least partially on how you end up seeing the quality of your life as you get older, but definitely frames the decision to continue screening in a totally different light.

I need a decision!

Cancer touches everyone, even if it’s not in your immediate family. As with all things cancer and screening, choices depend on your own values. For some women, the risk of stress, and possibly undergoing treatment that turns out to be not-needed is a small price to pay for ongoing peace of mind, and/or detection, even if the risk of what turns out to be not-needed treatment climbs as your “screening time” marches on. For other women, 10-20 out of 2000 women screened for 10 years, being treated for a breast cancer they didn’t have is an unacceptable risk. It’s one thing to say, “Well, that’s less than 1 percent,” but when it’s you, it’s 100% you.

For others, it’s a calculated risk of “not yet”, particularly if they are in their 40’s, and at least one set of guidelines (the Canadian ones) agrees that mammograms before the age of 50 are not recommended. And for others still, it’s “not anymore” as they pass into their 70’s and beyond where having to go through treatment for breast cancer might be far less appealing.

Sometimes science doesn’t give us hard, absolute rules, and even when there seem to be hard, absolute rules, personal values always affect decisions on health. There is no single right answer, but there’s an answer that is right for you. Science isn’t a dictator, it’s more like a friend. In this case, though, it’s a pretty indecisive, kinda douchey kind of friend who can’t pick a restaurant.

This opinion does depend on whether you are considered at average or high-risk for breast cancer and the research presented here only applies to women of average risk. If you’re not sure where you fall on the risk scale, your doctor is a great place to start.


1. Gøtzsche PC, Jørgensen KJ. Screening for breast cancer with mammography. Cochrane Database of Systematic Reviews 2013, Issue 6. Art. No.: CD001877. DOI: 10.1002/14651858.CD001877.pub5.

2. Kösters JP, Gøtzsche PC. Regular self‐examination or clinical examination for early detection of breast cancer. Cochrane Database of Systematic Reviews 2003, Issue 2. Art. No.: CD003373. DOI: 10.1002/14651858.CD003373.

3. Gartlehner G, Thaler K, Chapman A, Kaminski‐Hartenthaler A, Berzaczy D, Van Noord MG, Helbich TH. Mammography in combination with breast ultrasonography versus mammography for breast cancer screening in women at average risk. Cochrane Database of Systematic Reviews 2013, Issue 4. Art. No.: CD009632. DOI: 10.1002/14651858.CD009632.pub2.

4. Fitzpatrick-Lewis, D., Hodgson N., Ciliska, D., Peirson, P., Gauld, M., Liu, Y.Y., Breast Cancer Screening. Canadian Task Force on Preventative Health Care, 2011.

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