Mammogram Mania

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You wouldn’t know it from the pink billboards but questions about the benefits and risks of screening mammography have been ongoing in the medical scientific community for decades. No screening test has been studied more extensively, and study after study confirms that the vast majority of women (70 to 90%) do not have their lives lengthened as a result of routine screening. What’s more there’s a good chance they will be overdiagnosed (5 to 50 percent) and over-treated (20 to 30 percent), sometimes for conditions that are not life-threatening. None of this is news in the research community. Yet it wreaks havoc within the realms of advocacy, mass media, and public health.

An article in the Annals of Internal Medicine back in 1976 reviewed existing clinical and experimental data to discern whether screening mammography for entire populations made sense. At the time there was little data on the long-term effects of mammography or the inherent risks associated with radiation. It concluded that “promotion of mammography as a general public health measure was premature, that the possible benefits of mammography received more emphasis than its defects, and that the evidence that mammography alone played a significant role in the reduction of breast cancer mortality was weak and indirect.” That was 35 years ago. Since then there have been numerous studies of screening mammography, including randomized clinical trials and statistical modeling, all of which are designed to analyze the impact of routine screening on the primary end in mind–mortality reduction. What does the bulk of the data find? Mortality reduction as a result of routine screening is weak and indirect.

Seven major clinical trials were conducted between 1963 and 1982 that involved over half a million women. In 2000 the Lancet published the first systematic review of these trials, which assessed their quality in terms of agreed-upon standards for well-conducted and reliable research and also evaluated the findings. Researchers identified no trials with high-quality data and and two trials that were highly flawed (Edinburgh and New York). The remaining trials had either medium-quality (Canada and Malmö) or poor-quality data (Göteborg, Stockholm, and Two-County). When taking the methodology into account they concluded that there was no reliable evidence to justify mass screening of entire populations of women. These studies were then evaluated in greater detail and reported in the Lancet in 2001. The best conclusion was that mortality reduction due to routine screening was about 15 percent for women ages 50 to 69. The remaining 85 percent died at the same rate as unscreened women who developed breast cancer. Two additional meta-analyses of these seven clinical trials (2002 Humphrey review and the 2006 Armstrong review) also concluded that reductions in mortality resulting from mammography screening were quite variable, and fairly modest.

The Institute of Medicine reviewed breast cancer detection technologies too, releasing a report in 2001 called Mammography and Beyond. These reviewers found that screening outcomes had not been assessed adequately, which confused the potential value of routine mammograms in reducing deaths. They also identified several problems with the technology, such as the fact that mammograms are very difficult to interpret in women with dense breast tissue (something especially common in pre-menopausal women); that dense tissue interferes with the identification of abnormalities thereby leading to higher rates of false-positive results (i.e., those that do not, upon biopsy, show the presence of cancer) and also higher false negative results (i.e., those that miss tumors that actually are cancerous). They also found that routine screening frequently gives inconclusive results and that the ability of current screening tools “to determine the lethal potential of breast abnormalities is crude at best.” A followup symposium in 2005 reported similar concerns and reiterated that the reduction in the relative risk of dying from breast cancer was somewhere between 20 and 30 percent depending on age at screening.

The National Cancer Institute took up the mammography question in 2005, not through the testing of clinical effectiveness but through the use of high-level statistical modeling. The Cancer Intervention and Surveillance Modeling Network (CISNET) used retrospective surveillance data to create statistical models to illustrate past trends and project future trends related to screening and mortality. Reports based on CISNET estimated that routine screening reduced mortality between 16 and 22 percent. Based on the confluence of increased screening and improved treatment the researchers concluded that the overall decrease in breast cancer mortality from 1990 to 2000 (i.e., averaging about 20%) must have been related to mammography. There is no way to know for sure. However, statistical modeling for assessing risks and benefits is quite different from using clinical trials that involve real people in comparison groups who are observed over a period of time. Without contextual information about disease profiles, patient demographics, treatment regimens, and quality of care the association between routine screening and the overall decrease in mortality is, unfortunately, only a correlation.

In general there has been a consensus across studies that routine screening reduces the total breast cancer death rate somewhere between 15 and 25 percent. However, a Norwegian study reported in the New England Journal of Medicine (2010) found that mammograms combined with modern treatment reduced the death rate by only 10 percent, and that the effect of mammograms alone could be as low as 2 percent or even zero. This study only included a two-year followup, and must be viewed within its national context. Norwegians are insured under a universal, tax-funded, single-payer health system that is notable in terms of providing an important safety net for the population. The risk of dying of breast cancer is declining in Norway and the current rates are at the same level or lower than European averages. However, this study illuminates a critical insight: improvements in treatments may be responsible for improved outcomes for some groups of women regardless of when, or how, their tumors were found. Women over age 70 who were exposed to the program’s multidisciplinary medical teams but did not undergo mammography, for example, had an 8 percent reduction in breast-cancer mortality. This would explain why more recent clinical trials in advanced countries with improved treatment regimes are likely to find lesser or no effect on mortality due to screening.

None of this data has had an effect on U.S. society’s overzealous commitment to mammograms. Quarrels that focus on whether to start having them at age 35, 40, or 50 (though important in their own right) serve to detract attention from the fact that the overall reduction in mortality from screening is quite low. Compare the benefits of routine mammography with that of screening for cervical cancer. The Papanicolaou (Pap) smear has been called “the best screening tool ever introduced for any cancer.” It not only reduces the incidence of cervical cancer by 90 percent by detecting pre-cancerous conditions but has led to a 70% reduction in mortality in developed countries. An article in the American Journal of Clinical Oncology reports that among women who are screened regularly, the Pap smear may have reduced cervical cancer mortality by as much as 99 percent. Now that’s a screening tool that works!

The success of the Pap smear sets the bar high for breast cancer screening. So far, routine mammography screening hasn’t measured up. Yet studies abound to find out whether the existing technology benefits a small, or smaller, percentage of women. A study of two counties in Sweden found a mortality benefit of a whopping 30 percent. Early detection campaigners jumped for joy with statements that the study reconfirms that mammography saves lives. We already know that screening saves some lives, but that it doesn’t save most. What is being celebrated here?

There is much to consider about the Swedish study in the context of the mountains of data that already exist about screening. First, the findings from the Swedish study were not stratified by age so nothing can be said about the benefits of screening for different age groups of women. Second, the study did not systematically evaluate outcomes related to false-positive and false-negative results. Third, the methodology has been questioned previously in terms of the comparison groups and it is not clear that breast cancer deaths were counted correctly. Fourth, as Dr. H. Gilbert Welch has pointed out the study did not take into account the advances in breast cancer therapy over the last two decades. Finally, would the Swedish findings be generalizable to a population such as our own that does not have universal healthcare? If all of these issues could be rectified, we would still have a situation in which the vast majority of women routinely screened for breast cancer (in the Swedish study, 70 percent) would see no survival benefit due to screening.

Yes, routine screening does save some lives: About 1 in every 2000 women who are screened. That’s an individual stroke of luck, not a public health strategy. Instead of researching the same screening tool over and over again to look for minute differences in mortality benefits that continue to tell us what we already know, why not invest those research dollars into learning how to prevent cancer in the first place or keep those who are diagnosed from dying from the disease? [See also Kathi Kolb’s essay on Betty Ford and the Status of Mammography.]

Added Note: The print advertisement below is a typical example within the breast cancer “awareness” realm. Featured in an October special issue, it leaves no doubt that routine screening is unequivocally good for women.

  • It claims that mammograms are successful in finding 90 percent of breast cancers but includes no information about how many results are inconclusive, false-positives, or false-negatives.
  • It suggests that that routine screening may “prevent and diagnose” though screening is clearly not a form of primary prevention.
  • The ad even puts the onus on women themselves as being personally responsible for doing the “one thing” that might help them to beat breast cancer.
  • It also relies on peer pressure to coerce women into doing what their friends are doing.
  • This common advertisement embellishes and even fabricates information in support of its product (mammograms) while omitting real information that could help women to understand the risks, benefits, and limitations of screening technology.

Such strategies may be expected in advertising. But how different are they from everyday awareness campaigns and educational materials given to women about breast cancer???

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10 comments to Mammogram Mania

  • Wonderful review of the data, and a poignant conclusion. I suspect that our fear of breast cancer leads us to look for a “silver bullet,” which is neither an effective individual strategy, nor a sound public health policy. Until we have a breast cancer screening mechanism as reliable as a PAP smear, we need to keep THINKING about both risks and benefits.

  • Perhaps what all of these studies point up most of all is our desperation. We have to settle for mammography because so far there isn’t another screening tool on the horizon that has been shown unequivocally to improve the situation. It’s what we’ve got. But surely we can do better. I’m also struck once again by how wildly uneven the situation is for effective screening tools for all types of cancers. Why don’t we have better screening for lung cancer, for instance, which continues to kill more men and women than any other kind of cancer? Why do we not have a better screening tool for pancreatic cancer, which has one of the worst mortality rates among all cancers? Makes no sense to me. And why has the mortality rate for metastatic breast cancer stayed about the same for the past three decades? We have a long way to go yet before we can celebrate any real triumph over breast cancer.

  • As usual Gayle you provide a thorough analysis of the issues. And whilst everybody else seems to be celebrating these latest findings you are quite rightly asking why, and continuing to demand better for all women. Thank you for this post.

  • Excellent analysis and arguments Gayle. I agree, the media headlines, especially in this area are very misleading. It is important to understand the real story behind the numbers and headlines.

    Keep up the great work. I believe that the media, organizations, and people in general are just beginning to become more aware and go deeper than the propaganda of the headlines and awareness campaigns.

    Would love for you to share your insights on this topic with the TalkAboutHealth community. This question would be perfect for this information – I hear a lot of different viewpoints on the effectiveness of mammograms. Have mammograms helped reduce mortality or increase lifespan?. And please do provide a link back to this blog post.

  • Hi Gayle,
    With respect, you write on an important women’s health topic, here. This isn’t just a political issue.

    My perspective, as an oncologist, is the mammography is very effective in detecting the majority of invasive breast cancer cases when it’s done properly. Most of my colleagues attribute the dramatic reduction in BC-related mortality in the US since 1985 to mammography combined with better treatments. Unfortunately, I think a lot of the journalists, public health experts and epidemiologists don’t appreciate the problematic and nuanced details of the meta-analyses published in the Annals of Internal Medicine in November 2009 and other, subsequent and related press.

    Not wanting to write a book here, I’ll keep this comment to three points you mention with which I take issue:
    1. About mammography being ineffective in young women with dense breasts: For the premenopausal age group, who usually have denser breasts, digital mammograms are much better because they allow the radiologists, without using more radiation (and, typically, using fewer rads) to better view possible lesions by adjusting the contrast, enlarging areas of concern, etc. on images that have already been taken. (Most published data purporting to show a lack of benefit in mammography don’t consider digital mammograms in younger patients.)

    2. The “fact” of 30 percent of mammography takers or BC diagnosis receivers being over-treated (I’ve seen this number thrown around quite a bit) is unsupportable in 2011, either way: When women receive care from appropriately-credentialed radiologists and well-trained oncologists, there is neither a 30 percent false positive rate nor a 30 percent over-treatment rate.

    3. The 2010 NEMJ mammography report, to which you refer, is deeply flawed: the mean follow-up was only 2.2 years, far too short.

    I respect your work and writing on the problematic aspects of the “pink” culture and profiteering, but I don’t think that issue should be blended with the scientific/medical issue, controversial as that may be, surrounding the benefits of breast cancer screening.

  • Thank you all for your comments. There are clear political, economic, public health, and personal interests involved in the push for routine screening. While they can be disentangled analytically, they are so entwined in public representations of breast cancer that their subtleties can be easily lost.

    As Elaine suggested, there are wide variations in the level of expertise among those who are reading mammograms. This a point the Institute of Medicine and others have also pointed out. This would increase the chances for inconclusive results, false-positives and false-negatives. Improving expertise in reading mammograms would likely lead to better results, and there are efforts to do so. Digital mammography, as Elaine also comments, is better than analog for viewing dense breast tissue. There is in fact a movement now to require the reporting of breast density with mammogram results so that it is clearer whether women would benefit from digital over analog. Unfortunately, digital has not been found to be any better than analog for women with less tissue density.

    I updated the overtreatment percentage from 30 percent to the range of 20-30 percent (since I’ve seen both) and included a citation to Dr. H.Gilbert Welch, who has written extensively on the overtreatment of breast cancer and other diseases. I have seen no reason to take issue with his analysis though overtreatment as a concept must be defined and quantified clearly.

    I also noted that the 2-year follow-up issue regarding the Norwegian study, which was the primary concern researchers had about its conclusions. Chief Medical Officer of the American Cancer Society, Otis Brawley, commented that the study was well done but that this followup issue must be considered.

    I must respectfully disagree with Elaine on the idea that discussions of the scientific/medical issues should be kept separate from discussions of pink culture and profiteering. The print advertisement I included in this post from a mammography center in Florida is quite typical in breast cancer advertising whether it is for mammograms or other pink ribbon products. The lines have been blurred. Unfortunately, information in these ads and even in materials given to women from their health providers typically fail to point out the risks, benefits, and limitations of routine screening in ways that are meaningful to women as they make their own decisions. Instead the mantra: “Get your mammogram; tell your friends” is about the extent of it.

    I am not opposed to screening mammography. For women at higher risk for breast cancer especially, there may even be a need to evaluate them younger than age 40. What I am opposed to is selling mammography as the wholesale solution to the breast cancer epidemic while omitting crucial information about the risks, benefits, and limitations of this diagnostic tool. If the reduction in mortality is only 30 percent or less depending upon the country, the context, the follow-up, the level of expertise of providers, and the individual profiles of the women (and this is a short-list of just a few caveats), then what are we doing for the remaining 70 percent? It is my hope that we will have a widespread discussion about this across sectors that have a stake in ending the breast cancer epidemic.

  • Actually, there are at least two non-radioactive screening techniques that are much better at identifying possible cancers than mammography – sonograms and MRI’s. After my sonogram, my practitioner knew that I had cancer (even though she kept it from me). MRI’s are very good at finding probable cancers, but they are very costly and thus not extensively used in “screening”.

    CT scans are also good, but the repeated high dose of radioactivity is a real problem. PET scans are also the best, but again you have the radioactivity and the extreme high cost.

    The real problem is that women (me included) have just accepted mammography as the standard because of widespread ignorance about the subject.

    The solution would be to “really” educate the general population and to demand better screening despite the cost.

    Case in point: One of my high school friends just posted of Facebook about how she finally had the courage to get a mammogram and everything turned out OK. I commented that mine was reported to me as OK too, even though I had cancer at the time. I told her to ask for the actual report and if she saw the word “dense” in the report anywhere to ask for an MRI. A few days later she commented back and said that even though her family history was not strong, her doctor agreed to send her in for an MRI.

    So many women think if it says you’re OK then you really are. I could just kick myself for being one of them.

    Dianne Duffy

  • There are no easy answers and I think one of the most important points is that the issue to screen or not, and how to screen, is becoming more of an individual issue. This will of course make it more difficult – it’s “easy” to make recommendations for the general public, not so much to make individual case-by-case recommendations. One problem is that often family history is used as a way to identify increased risk. There is no doubt that family history contributes, sometimes significantly, but many women newly diagnosed with breast cancer do not have a family history of the disease. Breast density is very important, and women need to know to ask about their breast density, as this information is often not included in the form letter that is sent from the mammography center. CT and PET are not great screening tools for breast cancer (although PET/mammography or PEM may have a limited role) and ultrasound and MRI may miss some findings that can be better detected on mammography. Remember right now we have no one perfect test! Keep the discussion with your physician open, know your family history, your breast density, and your body, and ask questions!

  • Gayle,

    This posting really is excellent. Thank you for all the useful information. In my case, a mammogram totally missed my cancer. I found it through a BSE as a subtle dimple (didn’t feel a lump). My breast tissue was so dense, a mammogram could not pick it up. Even the diagnostic mammogram showed the tumor, but it was barely visible.

    I had to argue to get the medical care I needed. The screening mammogram was useless. And you know what? The report for that initial mammogram said my breasts were really dense, so the results may not be accurate. Was there any encouragement of followup? NO. If the radiologist had his/her druthers, I would just conveniently go away, happy with the results of “negative,” even though I was really positive for breast cancer.

    I had to look out for my own health. If I hadn’t, I wouldn’t be blogging today.

"women urged to get screened because it might save their lives. But that’s only 1 possible outcome, and it’s the least likely one" @cragcrest

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