Diana Zuckerman, PhD, Brandel France de Bravo, MPH, and Jae Hong Lee, MD, MPH, Cancer Prevention & Treatment Fund
For several decades, women have been told that regularly scheduled mammograms for midlife women can help detect breast cancer early and save lives. However, there have been controversies; for example, two Danish scientists concluded in 2001 that using mammograms to screen for breast cancer did not save lives. One of those scientists has continued to publish articles questioning the benefits of mammogram screening for breast cancer and arguing that women are not sufficiently warned about the negative effects of screening. As a result of the media attention to those concerns, some women are wondering whether they should undergo regularly scheduled mammograms. While the Danish researchers have highlighted some important issues, we say the answer to “Should midlife women undergo mammograms?” is YES.
First, it is important to know what evidence there is that mammograms save lives. Six large clinical studies performed by researchers over several decades, incorporating data from hundreds of thousands of women in three countries, have shown that using mammograms to screen for breast cancer helps to prevent deaths from breast cancer-with decreases in the number of breast cancer deaths ranging from 13% to 45%. Only one large study, performed in Canada, showed no difference in the number of breast cancer deaths with the use of mammograms. Some scientists have criticized the design of the Canadian study because it compared mammography plus a physical examination by a doctor to physical examinations alone. This study design would tend to dilute the benefits of mammography since physical exams and mammograms will detect some of the same cancers. However, numerous studies show that regularly scheduled mammograms help to catch breast cancer in earlier stages, when the chances of a cure are much better and when treatment might require less extensive surgery that conserves the breast. That last point is important, because even if the Danish study were correct and mammograms do not save lives compared to physical exams, earlier detection combined with less extensive surgery would be a significant quality-of-life benefit.
The bottom line is that either mammograms or physical exams will help detect breast cancer, but mammograms can detect much smaller, earlier cancers, and many women have mammograms more often than they would have physical exams. Overall, research indicates that the benefits of mammography generally outweigh the risks, as long as mammograms are performed in accordance with federal regulations (as outlined under the Mammography Quality Standards Act).
What kind of a study did the Danish researchers conduct to come up with results so different from six out of seven clinical studies? For their 2001 study, Ole Olsen and Peter Gotzsche performed what is known as a meta-analysis. This type of study does not produce any new data, but instead reanalyzes previously published data-in this case, data from the seven large clinical studies already mentioned above. Meta-analyses have become increasingly popular, in part because they are inexpensive and relatively easy to perform: all that is needed are paper copies of previously published studies, a computer, and software. However, performing a meta-analysis also requires many subjective decisions by the scientists that can bias the results. For example, many researchers disagree with the decision by Olsen and Gotzsche to label certain studies “unreliable” because of small differences in average age between the groups of women receiving and not receiving mammograms. Those researchers argue that differences of a few months in average age between patient groups are not relevant in judging the validity of a study. As you can see, it is very possible for two different teams of researchers performing a meta-analysis of the same data to reach completely different conclusions.
In a 2009 article, Gotzsche and his colleagues propose revising patient information materials about mammography screening to make the risks clearer to women. Although he acknowledges that mammograms can save lives, he again emphasizes that it is “not clear whether screening does more good than harm” because mammography screening results in “overdiagnosis” and “overtreatment.” False positives cause emotional distress and may result in additional unnecessary exposure to radiation. In addition, women with non-invasive breast conditions, such as Ductal Carcinoma in Situ (DCIS), may undergo medically unnecessary mastectomies. He concludes that instead of decreasing mastectomies, breast cancer screening with mammography leads to more mastectomies.
If six out of seven large-scale clinical studies show that mammography screening saves lives, could Gotzsche be correct that the risks outweigh the benefits? His articles have received a great deal of attention because he has worked with the prestigious Cochrane Collaboration and because the articles were published in two prestigious British medical journals: The Lancet and the British Medical Journal. Publication in such journals tends to lend weight to a scientific report, but that does not guarantee the quality or true importance of the work. In the case of the meta-analysis, some journalists could not critically evaluate the results from this type of study. Most journalists, including those who report on health issues, are not scientists and do not have extensive medical research experience. That may explain why the news media overemphasized the importance of the Danish meta-analysis, causing concerns among thousands of patients around the world.
How Overtreatment Affects the Risk to Benefit Ratio
Although the importance of the Danish meta-analysis may have been overemphasized, the authors did raise very important potential problems with breast cancer screening using mammograms: unnecessary biopsies or overaggressive treatment. The use of mammograms to screen for breast cancer does result in more biopsies for lesions that look suspicious on mammograms but are not cancer. However, better training of radiologists and improved technology could reduce the number of unnecessary biopsies. Overly aggressive treatment is a well-documented problem, and not only because of mammograms. Many breast cancer patients undergo mastectomies when they are eligible for less extensive breast-conserving surgery. Women who have pre-cancerous conditions are often urged to have surgery even when experts believe “watchful waiting” or “active surveillance” is the more appropriate choice. It is important for patients to carefully discuss diagnostic and treatment options with their physicians. A second opinion is always a wise option, especially if any type of surgery is recommended.
A final important issue is that at the same time that mammograms improve the chances of early diagnosis, they also expose women to radiation, which certainly can increase the risk of getting breast cancer. For this reason, it makes sense to avoid unnecessary mammography, rather than assume that more mammograms are better than fewer. Women should not undergo mammograms more often than is necessary, and they should make sure that their exposure to radiation from mammography is as low as possible.
When considering whether the benefits of mammography outweigh the risks, it is important to weigh the risks and benefits of mammography as a technology separately from the risks of overtreatment. Overtreatment can be reduced if physicians are more cautious in their treatment recommendations and do a better job of communicating with their patients.
Should women younger than 50 and older than 75 get mammograms? Every year or every 2 years?
The risks and benefits of mammography vary depending on a woman’s age. In November 2009, the U.S. Preventative Services Task Force (Task Force) changed their recommendations for mammography. The new recommendations raised the year of regular screening for most women from 40 to 50, and changed the frequency from every year to every two years through the age of 74. For more information on the most recent mammography screening guidelines, click here.
Over the past decade, the recommendations for mammography screening have changed several times. Prior to 2002, the Task Force screening mammograms recommendations were similar to current recommendations: women under 50 were not recommended for regular screening, because cancer is less common in that age group, and mammograms are less accurate for younger women because their breast tissue tends to be denser. Screening mammography was not recommended for women over 69 either, because the costs appeared to outweigh the benefits: older women tend to face many life-threatening illnesses other than breast cancer.
Between 2002 to 2009, the Task Force issued mammography screening recommendations that broadened the age range beyond women 50-69, even though 50-69 is still the age group for which the evidence of benefits and reduced mortality is greatest. These guidelines recommended that women 40 and older undergo a mammogram every 1-2 years. The Task Force made this change based on evidence that screening women 40 and older could possibly reduce breast cancer deaths by 20-25% over a ten-year period; however, they also point out that on average, the risks and benefits of screening mammography between the ages of 40-49 are relatively even.
In 2009, the Task Force retracted these guidelines as further evidence revealed that screening mammograms before 50 has little benefit for most women, and may even be harmful. At this point, there is a general consensus supporting regular screening with mammography for women 50 and older, but some debate still exists as to whether women 40 to 49 should routinely be screened. The associated risks of screening-false positives, unnecessary anxiety, biopsies, and exposure to radiation-outweigh the benefits for some women, but for others the risk of cancer is great enough to override those risks. It is important to note that both the Task Force and the American College of Physicians acknowledge that certain women would benefit from earlier screenings (such as women who have a high risk for breast cancer). Both groups encourage an individualized approach to determining whether a woman’s risk of cancer between the ages of 40-49 justifies regular mammograms.
An alternative to mammograms is magnetic resonance imaging (MRI). Breast MRIs are, on average, more than 10 times as expensive as mammograms, but they are more accurate at detecting breast cancer in high risk women and do not expose patients to radiation. Research suggests that they may be an especially good option for young women who carry the BRCA1 or BRCA 2 gene mutation, which puts them at very high risk for breast cancer. For women under 35 years of age with BRCA1 or BRCA2, the harms of annual mammograms outweigh the benefits. MRIs show great promise but because of the expense and high number of false positives, they are not likely to be used for regular screening anytime soon, except among those women at greatest risk. A 2012 study of women under 30 years old with BRCA1 and BRCA2 mutations showed that the radiation they were exposed to from early mammography increased their risk of breast cancer. Women with the most radiation exposure had the highest risk of breast cancer. This research indicates that young women who carry these genes should be screened using methods that don’t use radiation, including magnetic resonance imaging (MRI) techniques. According to a 2004 article in the Journal of the American Medical Association, “…MRI-based screening is likely to become the cornerstone of breast cancer surveillance for BRCA1 and BRCA2 mutation carriers, but it is necessary to demonstrate that this surveillance tool lowers breast cancer mortality before it can be recommended for general use.”
The Danish study stirred controversy a decade ago and some experts continue to be highly critical of mammography screening, but scientific evidence still supports the use of mammograms every 2 years for women ages 50 and over. Similarly, there is widespread agreement that women younger than 50 who are at a higher risk of breast cancer because of gene mutations or other risk factors should be screened regularly, but the risk of mammography can be reduced for them by using screening devices with reduced radiation, or with MRIs. We now know that women who are carriers of the BRCA genetic mutation are likely to be harmed more than helped by yearly mammograms starting at age 25-30, because the higher exposure to radiation over their lifetime increases their chance of getting radiation-induced breast cancer that they may not have gotten otherwise.
For women between the ages of 40-49 who are not at high risk, the benefits and risks of mammogram screening are close to even, which is why there are differences of opinion among health care providers. On average, for women between 50 and 74, mammograms every other year contribute to early detection, which can translate into less aggressive treatment and fewer deaths from breast cancer.
All articles are reviewed and approved by Dr. Diana Zuckerman and other senior staff.
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