National Breast Cancer Coalition (NBCC) The Mammography Screening Controversy: Questions and Answers February 8, 2002 In response to questions we have received from our members, NBCC has developed this preliminary Question and Answer document to help the public understand the issues being debated around mammography screening. NBCC continues to take new questions and refine the answers on an ongoing basis. 1. What is mammography? A mammogram is an x-ray of the breast that can reveal abnormalities, such as a tumor, inside the breast. Mammography can be used for screening and for diagnosis. Diagnostic Mammography—is performed if a woman has symptoms of breast cancer, such as a lump that can be felt in her breast. Screening Mammography—is performed to attempt to detect breast cancer before symptoms occur (i.e. annual exams) in women without symptoms of breast cancer. 2. If my breast cancer was found by a mammogram, doesn't that mean that it saved my life? No, not necessarily. Women often find breast cancer when they notice the symptoms of the disease, such as a lump, pain, or discharge from the nipple. Without that mammogram, you may have found your breast cancer a few years later because of the symptoms. There is no way to know whether discovering your breast cancer a few years later would have decreased your chance of surviving the disease. Many women who have never received a screening mammogram survive their breast cancer. Also, many women who get regular screening mammograms eventually die from breast cancer (sometimes years after it was discovered by a mammogram). Stories about individual women (anecdotes) cannot prove that mammography is effective. This is why we need research studies. Scientists perform studies on mammography screening to see if it prevents some women from dying of breast cancer. (To learn more about the limitations of early detection methods, see NBCC's Position Statement on Breast Self-Exam.) 3. When does early detection of breast cancer save lives, when does it not save lives, and when might it be harmful? Breast cancer begins in the breast. But often, it spreads to other parts of the body and starts to grow in those places. When breast cancer spreads to a vital organ, such as the brain or the liver, it becomes life threatening. So, one of the ways to save a woman's life is to detect and remove breast cancer before it spreads to her vital organs. Unfortunately, a mammogram may not detect breast cancer early enough. By the time a mammogram detects cancer in a woman's breast, the cancer has been growing there for an average of 6 to 10 years. That is plenty of time for the breast cancer to spread to a vital organ and start to grow. It could be years before a woman knows that her breast cancer has spread. That is why some women with breast cancer die many years later, even though their cancer was detected by a mammogram and removed. There are also some types of breast cancers that will never spread to other parts of the body, and mammograms probably find many of these breast cancers. Detecting and removing breast cancers that would never have spread to other parts of the body does not save any lives. Unfortunately, doctors have not figured out how to tell which breast cancers will eventually spread and which will not. The result is that many women get treated for breast cancer when they may not need to be treated at all. 4. Can mammography really harm me? Mammograms are not "risk free." There are several ways that mammography might harm a woman. When mammograms find lumps that are not breast cancer, women often undergo unnecessary biopsies (surgery to remove a suspicious lump). Although breast biopsies are relatively simple surgeries, they can still cause distress, scarring and disfigurement. Also, if mammograms find breast cancers that are not actually life threatening, women will undergo unnecessary and/or inappropriate treatments. Breast cancer treatments, such as chemotherapy and radiotherapy, are toxic and should not be given to women who do not need them. (See NBCC's Analysis of the Lancet Meta-Analysis on Radiotherapy for Early Breast Cancer.) Finally, mammography may harm women in ways that are not yet known. Question #17 will discuss this issue further. 5. When does it make sense to screen women with mammography? Mammography screening programs should only be initiated if scientific studies prove that such programs benefit women (e.g. save lives), and that the benefits outweigh the risks. In addition, women who get mammography screening must have access to treatment. Mammography will not save any lives unless it is followed by appropriate treatment. 6. What is the best way to find out if mammography screening benefits women? The best type of study for examining mammography screening is a randomized clinical trial. In a randomized mammography trial, participants are usually split into two groups – one group of women receives mammography screening and one group of women does not (the control group). In this type of study, the women do not choose which group they are in. Instead, they are randomly assigned to one of the groups. The trial participants are observed for a number of years, and then researchers compare the number of women who die of breast cancer in each group to see whether mammography saves lives. The number of women who die of breast cancer is called breast cancer mortality. 7. Why is randomization so important? Proper randomization helps ensure that participants in each group have a similar range of characteristics (e.g. ages, races, socioeconomic status, etc.). Ideally, the only difference between the groups should be the fact that one group gets mammography and the other group does not. That way, if the mammography group has fewer breast cancer deaths, researchers can be fairly certain that this reduction in mortality was caused by mammography and not by some other factor. 8. Are all randomized trials the same? Some randomized trials provide more reliable results than others depending on how well they are executed. It is important that a randomized trial enroll enough participants to rule out chance as an explanation for its results. If a trial has too few participants, the margin of error* may be too big to draw any real conclusions from the study. However, (in some cases) if several small studies are executed well, the results of each can be combined together to give a more reliable answer with a smaller margin of error. This is known as a “meta-analysis” or a “systematic review.” * In political races, margins of error are often stated to help the public understand poll results. For instance, a poll might show that Candidate X has a 5% lead over Candidate Y. However, if the margin of error in the poll is bigger than 5%, it means that the poll information is largely useless. In order to make the poll's margin of error smaller, more people would need to be interviewed. 9. How many randomized trials have examined mammography? There are seven published randomized trials of mammography screening. The oldest of these trials, the New York trial, was conducted in the 1960's. 10. What are the trials called, where were they conducted and who participated? Four of the trials were conducted in Sweden, one was conducted in Canada, one was conducted in the United Kingdom, and one was conducted in the United States. The seven trials are known as: The New York trial or HIP trial - enrolled women ages 40-64 The Malmo trial - enrolled women ages 45-69 The Two-County trial - enrolled women over age 40 The Edinburgh trial - enrolled women ages 45-64 The Canadian trial (parts 1 and 2) - enrolled women ages 40-59 The Stockholm Trial - enrolled women ages 40-64 The Goteborg trial - enrolled women ages 39-59 11. What did the trials find? Two of these trials – the Malmo and Canadian trials – found that mammography did not benefit women. In these trials, the women who got mammography screening had the same breast cancer mortality as the women who did not. The other five trials found that mammography did benefit women and reduced breast cancer mortality by about 30% on average. Although a majority (five of seven) of the trials found that mammography is beneficial, we cannot simply conclude that mammography saves lives. First, the reliability and quality of each trial must be evaluated. Some trials may have been poorly carried out, and some trials may not be applicable to the general population of women. Also, it is important to note that a majority of trials does not necessarily represent a majority in the number of participants. Some trials may have had many more participants than others. 12. Has anyone evaluated the quality of the seven trials? Many scientists have critiqued these trials, however, the most thorough evaluation to date was recently conducted by Drs. Gotzsche and Olsen, Danish scientists affiliated with the well-respected Cochrane Collaboration. These scientists set out to review and evaluate all seven of the mammography trials to determine the quality of each. The authors had no conflicts of interest and were unbiased at the start of the review. Their findings were published in a recent issue of The Lancet medical journal as a "systematic review." The general public learned of this review last December when The New York Times published an article discussing the review's controversial findings. The findings of the systematic review prompted an independent panel of experts at the National Cancer Institute to conduct its own evaluation of the seven mammography trials. This panel of experts, called the P.D.Q. screening and prevention editorial board, is responsible for providing doctors and the general public with summaries of the research evidence that supports cancer screening and prevention tools. After reviewing the seven trials of mammography, the panel concluded that there is insufficient evidence to show that mammography screening prevents breast cancer deaths in any age group of women. The panel was chaired by Donald A. Berry, chairman of the department of biostatistics at M.D. Anderson Cancer Center in Houston, Texas. 13. What were the findings of the systematic review? Using standard criteria, the authors rated each randomized trial's quality with one of the following marks: high, medium, poor or flawed. Based on these criteria, they found that no trial was high quality; the Malmo and Canadian trials were medium quality; the Two-County, Stockholm and Goteborg trials were poor quality; and the New York and Edinburgh trials were flawed. The two trials with the best quality data - the Malmo and Canadian trials - did not show that mammography screening benefits women. The five trials that showed a breast cancer mortality reduction had serious problems, including: missing data and poor documentation of methods poor randomization methods differences in the characteristics of the mammography and control groups (e.g. age ranges, socioeconomic status, etc.) at the start of the trials exclusion of more women with previous breast cancer from the mammography group than from the control group bias in determining the cause of death 14. What does "bias in determining the cause of death" mean? It is more difficult than most people realize to accurately determine a person's cause of death. Some women who died in the randomized trials of mammography had two or three different types of cancers as well as other health problems. Data from the trials show that ambiguous causes of death were more likely to be labeled breast cancer deaths in the control group than in the mammography group. This may have occurred because some of the trials had an unblinded assessment of cause of death. In other words, the people deciding cause of death knew which group the deceased women belonged to and this knowledge may have influenced their assessment. In addition, many women were not autopsied. Finally, the type of breast cancer treatment that women received may have influenced the assessment of the cause of death. 15. How does the quality of mammography screening compare in each trial? The authors of the review point out that the trials which reported the largest mortality reductions: 1) used the poorest mammography equipment, 2) only invited women to two or three screenings, 3) had the longest intervals between screenings, and; 4) began screening the control group too soon. Thus, the quality of mammography screening in the Canadian and Malmo trials was good in comparison to the other trials. 16. Did the authors of the systematic review find any negative effects of mammography? Drs. Gotzsche and Olsen found that women who were screened with mammography had more false-positive results, more unnecessary biopsies and more aggressive treatment. A false-positive result occurs when a woman's mammogram shows a suspicious lump, but she actually does not have breast cancer. Mammography screening also increased the number of mastectomies by 20% and the number of mastectomies and lumpectomies combined by 30%. 17. Could mammography have more serious negative effects? It is possible that mammography could have life-threatening effects that are currently unknown. All of the seven randomized trials measured deaths from breast cancer only – not from other possible sources. If it turned out that mammography caused heart disease and hundreds of the trial participants died of heart disease, those results would not be represented in the trial findings. In order to determine whether mammography has any life-threatening effects, researchers should examine *overall* mortality (deaths from all causes) in randomized trials. Using overall mortality would also eliminate "bias in determining the cause of death" (see question #14) from the research studies. Unfortunately, none of the seven randomized mammography trials were designed to examine overall mortality. Part of the problem is that a study would need a very large number of participants to give reliable results for overall mortality. In addition, some of the data necessary for evaluating overall mortality is missing from the studies that were rated poor and flawed. Using the data that are currently available, none of the seven randomized trials showed an overall mortality benefit from mammography. 18. What are the conclusions of the systematic review? There were three main conclusions: None of the seven trials showed that mammography screening decreases overall mortality (deaths from all causes). The two best trials did not show that mammography reduces breast cancer mortality (deaths from breast cancer). Mammography leads to more aggressive treatment and more unnecessary surgeries. The authors do not state that there is proof that mammography is ineffective. But they do state that there is no evidence that it is effective. Finally, the authors suggest that, in order to get a definite answer, more randomized trials should be designed and conducted to determine mammography's effect on overall mortality. 19. Is there any way to get better answers immediately? Many scientists and researchers believe that if the individual patient data from all of the trials can be independently audited and analyzed, we will get clearer answers. Unfortunately, the researchers who conducted the four Swedish clinical trials have refused to divulge their data to the public, despite being called to do so repeatedly. 20. What can be done to help resolve the issues brought up in the systematic review? NBCC is leading a campaign to have the Swedish researchers release all of the data and documentation so others can conduct a thorough, independent audit of all of the trials. The Swedish researchers must provide individual patient data, data on deaths from all causes and complete accounts of the methods used. This crucial information will help resolve many of the concerns and questions raised by Drs. Gotzsche and Olsen, and may provide better answers about the effectiveness of mammography. 21. Wasn't there a recent study on mammography that found a large benefit from screening? Several months prior to the release of Gotzsche and Olsen's systematic review, an individual study of mammography was published in Cancer, a scientific journal funded by the American Cancer Society. In this study, the authors claimed that mammography screening prevented about two thirds (63%) of breast cancer deaths. The main author was a radiologist (a doctor who conducts mammograms) named Laszlo Tabar. Some people have been using this one study to defend mammography and counter the conclusions made in Gotzsche and Olsen's systematic review of seven randomized trials. However, the Tabar study had major shortcomings that call into question the reliability of its results including the fact that the study was an observational study, not a randomized trial. This study did not compare similar groups of women. The group of women that was screened was enrolled and observed many years (in some cases up to 29 years) after the unscreened group of women. Therefore, comparing these two groups is like comparing apples and oranges. Finally, treatments for breast cancer have improved in the past few decades, so treatment, rather than screening, may have been largely responsible for the decrease in breast cancer deaths observed in this study. 22. Have there been any other analyses of mammography recently? The Malmo trial is one of the seven randomized mammography trials, and its quality was better than most of the other trials (see question #13). Originally, the Malmo trial did not show that mammography reduced breast cancer mortality significantly. In the February 2 issue of The Lancet medical journal, several authors published an analysis that takes a closer look at the Malmo trial. They argue that the benefits of mammography screening probably do not appear until years after women receive the screening. Thus, they examined the breast cancer mortality rates of women starting with the eighth year of the study onward. The authors' analysis indicated that, in women between the ages of 55 and 69, from the eighth year of the study onward, there was a breast cancer mortality reduction in the group of women that received mammography. This analysis is of questionable value. When a scientist examines small subgroups within one study, the results can be unreliable. The Malmo study was not designed to answer questions about a small age group of women during a very specific number of years. It is not scientifically valid to pick apart the data of a study in order to prove a point when the study was not designed to prove that point. Finally, this new analysis did not examine overall mortality (deaths from all causes). 23. What is NBCC’s position? NBCC has long questioned the limitations of mammography screening. For years, NBCC has said that mammography is not the answer to the breast cancer epidemic. Although it may be difficult to accept, it is vital that women know the truth about breast cancer screening and the false sense of security it provides. As breast cancer activists, the Coalition welcomes the long overdue criticism and discussion of the effectiveness of existing breast cancer screening methods. We must accept that we do not know how to detect breast cancer truly early, how to prevent or cure this disease, and focus our attention on getting those answers. The goal is to focus research efforts on true prevention – stopping breast cancer from occurring altogether – and on new, more accurate ways to detect and treat breast cancer. About NBCC The National Breast Cancer Coalition is a grassroots organization dedicated to ending breast cancer through the power of action and advocacy. The Coalition’s main goals are to increase federal funding for breast cancer research and collaborate with the scientific community to implement new models of research; improve access to high quality health care and breast cancer clinical trials for all women; and expand the influence of breast cancer advocates in all aspects of the breast cancer decision making process. www.stopbreastcancer.org National Breast Cancer Coalition 1707 L Street, NW, Suite 1060 Washington, D.C. 20036 (202) 296-7477 voice (202) 265-6854 fax © 2000 LINK Remember we are NOT Doctors and have NO medical training. This site is like an Encylopedia - there are many pages, many links on many topics. Support our work with any size DONATION - see left side of any page - for how to donate. You can help raise awareness of CAM.