Mammography Screening—Both Good and Bad News
Mammography screening seems destined to spawn controversial study results, as it has in the last few months. And its role in reducing the breast cancer death rate will remain the subject of heated debate among researchers for a good long time. The U.S. breast cancer death rate has declined 20% since 1990, as it has in other western countries. But it is not clear whether this can be credited to mammography, treatment improvements, or simply greater awareness among women that breast tumors should be promptly examined. What has become increasingly clear is this: Mammography screening harms more women than it helps.
That’s not the message that goes out to women via the media and their doctors. Of the three recently published mammography screening studies, the most media attention went to the one that seemed to equate the improvements in breast cancer survival with the increase in the proportion of women now diagnosed with small breast cancers. That was the take-home message from a CNN TV interview with Clifford Hudis, MD, a co-author of this study published last month in the journal Cancer.
With his colleagues at Memorial Sloan-Kettering Cancer Center, New York City, Dr. Hudis reviewed the early-stage breast cancers diagnosed in the U.S. over a 24-year period, from 1975 to 1999. The statistics came from the government’s database that draws from nine cancer registries across the country considered to be broadly representative of the U.S. population. Information concerning more than ¼ million breast tumors from the same population was also available to the researchers. The upshot: Many more small breast cancers were diagnosed in 1999 than were diagnosed in 1975.
Certainly sounds like good news, and that’s how it played out in the Wall Street Journal and other media. Yet despite the messages conveyed in the CNN TV interview, Dr. Hudis’s study did not determine why the breast cancer death rate went down. It simply found a greater number of women diagnosed with breast cancer in recent years had small tumors.
It is unclear why Dr. Hudis would misrepresent his own study and leave CNN viewers with the impression that mammography and breast self-examination (BSE) are largely responsible for the decline in breast cancer deaths. Let’s put aside for the moment Dr. Hudis’s discredited belief in BSE, as two trials showed the practice leads to unnecessary biopsies with no discernible benefit.
Instead, a hard look at the nation’s increase in small cancers is long overdue. The topic is too complicated for a four-minute TV interview. The breast cancer death rate may be going down, but there has also been a steady annual increase in the number of women diagnosed with breast cancer over the last two decades. The increase is generally acknowledged to be related, at least in part, to mammography screening. This is not entirely good news. Mammography screening may prolong life for some women, but it also causes many more women to be diagnosed and treated for cancers that they would be better off not knowing about. Not all cancers are deadly even if left undetected.
“Screening mammography is great for finding small cancers. But finding small cancers is not necessarily good,” according to Donald Berry, PhD, Chair of the Department of Biostatistics and Applied Mathematics at the University of Texas M.D. Anderson Cancer Center. In an e-mail interview, Dr. Berry explained that breast cancer comes in several different forms. “Some cancers are lethal and others are not. Non-lethal cancers tend to be smaller, and they tend to grow more slowly.” Dr. Berry recently co-authored a study that showed that breast cancers detected by mammography tend to have the best prognosis (excellent chance of recovery with treatment), even when the cancer has spread to the lymph nodes. The authors advise doctors to take that into consideration when recommending treatment.
Dr. Berry and colleagues assessed the outcomes of two major mammography screening trials that together included over 150,000 women, singling out those who eventually developed breast cancer. More cancers—both invasive and noninvasive (ductal carcinoma in situ)—were detected among mammography-screened participants, as compared with those not given mammograms.
“Screening mammography finds a greater proportion of non-lethal cancers than do other methods of detection. Unfortunately, it is not possible to perfectly identify which cancers are lethal. So we treat them all. Consequently, screening leads to overdiagnosis and excessive treatment,” Dr. Berry explained, referring to surgery, radiation, hormonal therapy, and chemotherapy that some women could have avoided without risking their health. Unfortunately, women have been led to believe the opposite—that mammography leads to less drastic treatment.
One of the trials assessed by Dr. Berry and colleagues found the breast cancer death rate among the women given mammograms was no different from that of the women not given mammograms. This is after 16 years of followup. The finding clearly suggests that mammography is not only useless but harmful to a significant number of women. There were 82 additional breast cancers* (half were invasive and half were noninvasive) in the women given mammograms. In other words, 82 of the mammography-screened women were treated for a cancer, including invasive cancer, which would not have produced symptoms or become life-threatening.
No other cancer screening test has been as well studied as mammography. Of the seven such trials conducted worldwide, two found no difference in the breast cancer death rate between the mammography-screened women and those not given mammograms. In a systematic review of the seven mammography trials conducted in 2000 by the Cochrane Collaboration, the two trials that found no life-prolonging benefit to mammography were determined to be superior in terms of quality than the five trials that showed a modest benefit to mammography. (None were without flaws.) The Cochrane Review’s conclusion: “Screening is unjustified.”
The merits and flaws of these seven major trials have dominated the controversies over the value of mammography. Little is known about the quality of mammography screening in the real world. Women who participate in clinical trials are given high-quality mammograms that are read by experienced radiologists. In other words, it is mammography under the best of circumstances. Not enough research attention has been given to the question of how women fare when given mammograms in the everyday practice of medicine. That was the point of a new study led by Joanne Elmore, MD, School of Medicine, Harborview Medical Center, University of Washington, Seattle.
With colleagues at several medical centers, Dr. Elmore looked at the medical records of women enrolled in six health plans around the country. They singled out the women who died from breast cancer between 1983 and 1998, an era that followed major improvements in mammographic techniques. 1351 women with breast cancer (aged 40 to 65 years) were matched with 2501 cancer-free women who were the same age and with the same level of risk for breast cancer.
Dr. Elmore and colleagues compared the screening practices (mammography and a physician’s breast exam) of the women who died of breast cancer with the high-risk women who were still alive. High-risk was defined as having a family history of breast cancer or a breast biopsy, as noted in the medical records. If screening reduces the rate of breast cancer death, the researchers expected to find that the women who died of breast cancer had undergone less screening then the women still alive. In fact, there was no difference between the two groups. “Our findings suggest that breast cancer screening in the community was minimally effective in preventing death,” concluded Dr. Elmore and colleagues. Results were published in the Journal of the National Cancer Institute.
In the editorial that accompanied this study, Russell Harris, MD, University of North Carolina, Chapel Hill, gave several reasons why screening may be making “a smaller contribution” to the reduction in breast cancer deaths than the major trials have led us to believe. “Better treatment may mean that screening is less necessary than it was previously, because treatment of later stage cancers may still be effective.” He also cites the fact that women today are more likely to have breast lumps “found accidentally” promptly examined by a health professional. Here Dr. Harris is referring to women finding tumors while in the shower, as opposed to finding them while doing BSE.
Women continue to get one-sided information about mammography (“it will save your life”) and little about its harms (unnecessary treatment). This was reflected in a survey of American women’s attitudes toward this technology in 2000. Only 6% reported that they knew about cancers that do not progress or become life-threatening.
For an international perspective on the accuracy of the mammography information dispensed to women via Web sites in eight countries, a 2003 survey was conducted by Karsten Juhl Jorgensen, MD, and Peter C. Gotzsche, MD, of the Nordic Cochrane Center in Copenhagen. They assessed 27 Web sites that were sponsored by governments, professional organizations, and consumer advocacy groups.
Jorgensen and Gotzsche, whose findings appeared last year in the British medical journal, BMJ, concluded, “The information material provided by professional advocacy groups and governmental organizations is information poor and severely biased in favor of screening…and failed to mention major harms.” On the other hand: “Web sites of consumer groups were more balanced and comprehensive.” The three consumer advocacy groups with the balanced information are all U.S.-based: The National Breast Cancer Coalition (www.stopbreastcancer.com), Breast Cancer Action (www.bcaction.org) and the Center for Medical Consumers (www.medicalconsumers.org).
Based on the findings from seven clinical trials, Jorgensen and Gotzsche describe the cost to women in terms of unnecessary treatment. For every 1000 women who undergo mammography screening for ten years, they report, one woman will have her life prolonged; five additional women will receive an unnecessary cancer diagnosis and treatment; and three women will have a benign tumor biopsied.
“Whether this is too high a price to pay is open to debate,” wrote Jorgensen and Gotzsche, “but if women and policy makers are not informed of this balance between major benefits and major harms—which they have not been so far—then there cannot be any discussion or rational decision making.”
Bottom Line: Mammography-detected breast cancers have the best outlook. The screening test also leads to the detection and treatment of breast cancers that would never become life-threatening. Mammography’s role in the nation’s declining breast cancer death rate remains unclear. At best, it appears minimal. Women are not receiving honest information about mammography’s harms.
*There were 592 cases of invasive breast cancer and 71 noninvasive breast cancer in the approximately 25,000 women given mammograms, as compared with 552 invasive and 29 noninvasive breast cancers in the approximately 25,000 not given mammograms. The women were age 40 at the start of the trial. Only half of all noninvasive cancers, also called ductal carcinoma in situ, are likely to become invasive, but all are treated as if they will. This trial indicates that invasive cancers do not always progress and become lethal.
Maryann Napoli, Center for Medical Consumers ©