Preventing Breast Cancer Deaths – How Much Credit Does Mammography Get?

Much less, it appears, than we’ve been giving it.

So say researchers who measured breast cancer mortality before and after the introduction of routine mammography screening in Norway. They compared breast cancer death rates between two groups of women in their 50’s – those who were offered routine mammograms and those who were not – between 1996 and 2005.

Their thinking goes something like this – If mammography prevents breast cancer mortality, then women who were offered mammograms should have fewer breast cancer deaths now compared with historical rates before mammogram screening was offered. And they did – about 7 less deaths per 100,000 person-years (the so-called screening effect in that chart up  there).

But here’s the rub – women who did not have screening mammography also had less deaths than their historical counterparts – about 5 less per 100,000 person-years. (The so-called time effect)

This means that the mortality reduction credited to mammograms is about 2 per 100,000 person years, or about a 10% reduction in breast cancer deaths. The lion’s share of mortality reduction appears to be due to advances in breast cancer treatment and possibly medical care in general, something researchers have long suspected but have been unable to prove.

What do the Critics Say?

Experts at the American Cancer Society have criticized some aspects of this study. They point out that while mammography had little impact on mortality in early stage breast cancer, the impact on stage 2 disease mortality was significant. They also criticize the very short follow up period of the study – an average of 2.2 years. Finally, they cite the lack of control of subject behavior (or “contamination” as women may have accessed mammograms outside the national program), and the fact that Norway’s mammogram screening program coincided with a national program of multidisciplinary breast cancer treatment that is not in place in the United States, making mammography potentially more important here.  The ACS continues to recommend annual mammgraphy in average risk women starting at age 40.

The accompanying editorial in the New England Journal of Medicine takes a a different tack, and suggests that the decision to preform screening mammography is, in fact, “a close call”, but stops short of actually making the call.  (I encourage you to read the editorial – it summarizes well the results, strengths and limitations of the Norwegian study.)

My Take

I’m not sure that we should use the results of this population-based data to refute the results of randomized trials, which have shown mammography to reduce mortality by about 25% in women ages 50-59.  In evidence-based medicine, the randomized trials tend to win out.

Still, the data presented make a compelling argument that on a national scale, mammograms may have had limited impact compared with advances in and coordination of breast cancer treatment.

I’ve raised the question before as to whether mortality should be the only bar against which we measure mammography. I wonder if women who get diagnosed with breast cancer on screening mammography have more very early stage disease, more options for localized therapy instead of mastectomy, or less use of chemotherapy than women who do not have mammgorams routinely? I’ve yet to see much discussion on this issue among the decision makers on mammography, but suspect it’s an important consideration for women.

What I’m Doing in My Practice

I’m continuing to recommend screening mammography in women ages 50 and above, and in high risk women at an appropriate age depending on family history. This study is raising important questions for that group, and is sure to generate a few phone calls and fuel some discussions during office hours, but I’m not changing my recommendations just yet in this age group.

For average risk women under age 50, I’ve recently begun to have individualized discussions about the screening mammography, and learning that it’s not an easy discussion to have. To that end, I initiated a project with my colleagues here at Cornell and at Memorial Sloan Kettering Cancer Center to begin to develop tools to assist women and their clinicians in having informed discussions about mammography. We just got a small pilot grant – wish us luck!
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Last updated 09/23/10

9 Responses to Preventing Breast Cancer Deaths – How Much Credit Does Mammography Get?

  2. Hi TBTM – I wanted to send you a direct message via twitter, but even though I am following you ..you aren’t showing up in Direct messages. ?

    I have friends that say mammos aren’t good because of the radiation and squeezing the breasts. Is that true?

    I always get them when told to. I am due now. 🙂 I don’t do the self breast exams. A surgeon I went to in 06 to have a lump checked (it was nothing),said that a studies show self breast exams don’t make a difference in preventing cancer. I was never good about them and so didn’t stop because of his statement.

    But ..the exams by the gyne docs seem to be so fast ..I do wonder how they could really feel anything and know the difference unless extremely obvious. Actually ..i would think women would be aware of more if they consistently did the self exam. As far as radiation ..personally I’ve had so many abd cts ..that mammos are the least of my concerns ..unless the radiation to the breast could activate a cancer process. ?
    ****************
    My direct question was going to ask about Cornell physicians and Sloan Kettering. Would it be alright if I ask here? With the understanding that you may prefer not to answer ..although it is a general ..anyone may be interested question.
    ********************************
    In coming over here to see if you have e-mail I read your “Ask a Simple Question” post. HILARIOUS!

    Would it be alright if I put it up in it’s entirety as my next post,link to it and tell everyone that the comments to this post are also very funny ..or something like that?

    Either way ..thanks for the laugh – that was great! 🙂

    Reply

    • Hi SeaSpray-
      Mammos do expose the breasts to radiation and that must be factored into the risk-benefit equation for the test. Don’t worry about the squeezing pat though. (ouch!)

      Probably best to leave institutional specific questions off line – email me.

      Feel free to excerpt or link to my posts but I would ask that you not post them in their entirety.

      Thanks for reading and good to hear from you!

      Peggy

      Reply

      • Thanks TBTM. Okay ..I will still link to it. I’ll just put a little teaser because I know people don’t always follow links. Ha! Although if sex is mentioned ..probably an enticer for sure.

        I didn’t see an e-mail address. It’s probably right in front of me. But where?

        And YOU are the one person …who explained menopause ..the one day marker thing and I have since explained it to other women. Amazing that so many women don’t really understand something so important.

        Your welcome and you have a great blog. 🙂

        Unbelievable that I am by definition …still peri-menopausal. But I do think that this might be the last 6 month stretch toward *the* day. 🙂

        Reply

  4. You provide a clear picture, and outline, of the Norway mammography trial results. But the critique’s important, too. Two years is far too short an average follow-up period after diagnosis in breast cancer, as you point out. Oncologists (and, unfortunately, patients) are keenly aware that this condition, when it recurs, often does so after an interval of years.

    Despite the editorial’s claims, there is still little published data regarding the efficacy of digital screening mammograms every other year for women above the age of 40 in the 21st Century – in the context of modern pathology, decision tools and current treatments.

    Reply

  5. There was an article in the Post this morning about some NP who is turning down mammograms becuase of this finding. I say fine — it’ll make it easier for me to make my yearly appointment!

    I totally agree with your perspective that having your breast cancer dealt with at the earlest stage possible has value beyond the simple mortality statistic.

    Chemothearpy is not the end of the world but it does come with uncomfortable side effects plus considerable expense. If early detection can help a woman skip it then, IMO, it’s all worth it.

    Reply

  7. Hi, This is Doug I ran across your blog and really enjoyed looking at. I wanted if ask if it was of to link to your blog from mine. I haven’t done this yet, I just read it Blogger’s courtesy to ask first. Mainly because I wanna talk a lot on health and food, but there is only so much I can write about women’s health, thus I wanna to have some links to some really good female written blogs.
    my page is http://www.gaiahealthblog.com
    Regards,
    Doug Wallace, Portland Oregon

    Reply

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