The Case for Mammography: What One Flawed Study and Critics of the Exam Don't Address
In their September 20, 2000 issue, the Journal of the National Cancer Institute published the most recent results of a highly controversial study. These results stated that mammography does not improve breast cancer patient survival any more than physician-performed clinical breast exams (for women in their fifties). The study was conducted by the National Breast Screening Study of Canada (NBSS) and received an onslaught of media attention at the time of its publication (click here to read more about the NBSS study).
Individuals and organizations who do not support widespread screening mammography for women 40 years of age and older continue to use the study as "evidence" that mammography is not effective or necessary and to support the claim that because mammography uses radiation, it may do more harm than good. Consequently, women who are apprehensive about having a mammogram in the first place are being encouraged to embrace their fears and forego mammography—even though a multitude of data collected over 30 years shows that the exam could quite possibly save their lives.
It is important to note that the results of the NBSS study are not widely accepted by members of the medical community and that several organizations, including the American Cancer Society and the Susan G. Komen Breast Cancer Foundation, have published articles to encourage women 40 years of age and older to keep receiving annual mammograms in order to detect breast cancer at an early stage, when the chances for successful treatment and survival are the greatest.
In an effort to provide a complete and accurate depiction of the role of mammography in the breast cancer detection process, the Imaginis.com Breast Health Team has taken a few of the most frequently cited arguments against mammography and clarified specific points in these arguments in the form of rebuttals. A list of additional resources and references follows these arguments and rebuttals.
Argument: Since the NBSS study shows that breast cancer detection with mammography does not increase patient survival any more than detection with physician-performed clinical breast exams, then annual screening mammography is not necessary.
Rebuttal: The NBSS study is considered flawed by several top U.S. breast imaging experts. Interestingly, this study is the only research that is repeatedly cited by skeptics of mammography. If the data in the study are valid, there should be many more studies corroborating the findings. Organizations that supported annual screening mammography for women aged 40 and older before the study was published continue to support those guidelines now. These organizations include the American College of Radiology, the American Cancer Society, the American Medical Association and the American College of Surgeons.
In an interview with Imaginis.com last October, Robert Smith, PhD, Director of Cancer Screening for the American Cancer Society, identified several problems that lead to the conclusion that the NBSS study should not be considered valid. First, the women in the NBSS study received intensive, high quality clinical breast exams by highly trained nurses, which are not representative of the typical clinical breast exam a woman receives. Secondly, the quality of mammography equipment used in the study was poor and mammography was performed and interpreted by technologists and radiologists with no specific training in the procedure. Third, the process of randomization [in the NBSS study] appears to have failed; a higher than average percentage of women with advanced breast cancers were randomly assigned to the mammography group.
"But perhaps more to the point," said Dr. Smith, "several decades of research have shown us that it is an indisputable fact in the large majority of cases—that the earlier breast cancer is found, the better the prognosis. The finding that there is no difference between mammography, which detects non-palpable [unable to be felt] breast cancer, and clinical breast exams, which detects palpable breast cancer [able to be felt], is truly counterintuitive," said Dr. Smith.
Argument: When mammography detects breast cancer, the cancer has already been growing for several years. Thus, mammography does not "detect cancer early," as many experts claim.
Rebuttal: It is true that cancer may be present but undetectable for a period of time before it is noticed with mammography. However, breast cancers have been growing for years by the time they are detected regardless of what method of detection is used. Simply because the cancer has been present for years does not mean that nothing is gained by treating it as soon as possible. In many cases, mammography can detect breast cancer long before a lump can be felt by hand. However, this is not always the case. That is why is it equally important that women 40 years of age and older perform monthly breast self-exams and have annual regular physician-performed clinical breast exams in addition to annual screening mammograms. The American Cancer Society recommends that women younger than 40 years of age also practice monthly breast self-exams and receive physician-performed clinical breast exams at least every three years. Mammography, like all medical tests, has its limitations, but currently, it is the most practical and cost effective breast cancer detection method available.
Argument: Because mammography misses breast cancers in some women, it is not a practical screening tool.
Rebuttal: Mammography is the most accurate screening tool for breast cancer and should be used in conjunction with monthly breast self-exams and regular clinical breast exams. While the vast majority of breast abnormalities are detected by mammography, some are simply not detectable. Some cancers are extremely aggressive and can metastasize (spread) to other areas of the body before they are detected by mammography. In general, breast cancer has a slow rate of growth. It may take six to eight years for a breast cancer developing from one cell to grow to the size of one centimeter. This long growth period allows ample time for aggressive cancers to spread into blood vessels, lymphatic vessels, and beyond the breast.
Mammography finds approximately 85% of all breast cancers, which makes it the most practical breast cancer screening modality available today. Mammography can detect breast cancer in its early stages, often before a lump can be felt by physical examination. Therefore, annual screening mammography is recommended for all women once they reach 40 years of age.
Furthermore, microcalcifications, tiny calcium deposits in the breast whose presence is often an early sign of breast cancer, can be seen reliably with mammography. About half of the cancers detected by mammography appear as a cluster of microcalcifications. Other supplemental breast imaging exams such as breast ultrasound, magnetic resonance imaging (MRI) of the breast, sestamibi nuclear medicine breast imaging (scintimammography), and T-scan (electrical impedance imaging) do not image calcifications as well as mammography. These supplemental exams do not provide the fine detail (spatial resolution) that is available with conventional x-ray mammography. However, these adjunct exams are beneficial because they can provide excellent contrast resolution, which may make some abnormalities easier to see since these areas "stand out" more from surrounding tissue. Therefore ultrasound, MRI, nuclear medicine, and T-scan may be used as supplemental tests in conjunction with mammography in an attempt to confirm or rule out the presence of malignant tissue.
Argument: Radiation itself is known to cause cancer. Because mammography exposes patients to radiation, the exam poses risks to women.
Rebuttal: "There is no data to suggest that mammography, in its current dosage, poses any measurable risk to women," said Bruce Schroeder, MD, Clinical Assistant Professor of Radiology at East Carolina University School of Medicine, Pitt County Memorial Hospital and Medical Director of Eastern Radiologists Breast Imaging Center in Greenville, North Carolina.
Modern mammography systems use extremely low levels of radiation: usually about 0.1 to 0.2 rad dose per x-ray (rad is the scientific unit of measure of radiation energy dose). To put the mammography dose into perspective, a woman who receives radiation therapy as a treatment for breast cancer will receive several thousand rads. If a woman had annual screening mammography for 50 years (two x-ray views per breast), beginning at age 40 years and continuing until age 90, she will have received a total of 10 rads to 20 rads per breast over the course of 50 years.
Argument: Most breast lumps are found by women themselves. If they present the lump to their doctor but a subsequent mammogram reveals nothing, they are often sent home with no further follow-up. Thus, screening mammography is not an effective tool for detecting breast cancer.
Rebuttal: Unfortunately, this scenario does happen from time to time. However, it is not the accepted standard of care. By definition, a screening mammography is performed to look for breast cancer in women who do not show any signs or symptoms of the disease. If a breast lump is palpable (felt by touch), a patient does not typically receive screening mammography; she receives diagnostic mammography. Diagnostic mammography involves taking additional views of the breast and is much more time-consuming than screening mammography. In addition, breast ultrasound often plays an important role in the breast cancer diagnostic process.
It important to note that the majority of breast lumps are not cancerous. However, all palpable breast lumps should receive clinical follow-up or biopsy, even if a mammogram does not reveal an abnormality.
Argument: Because clinical breast exams are integral to the breast cancer diagnostic process, physicians and nurses should be better trained in performing physical exams.
Rebuttal: No rebuttal. This is absolutely correct. Physicians and nurses should receive extensive training so they are able to perform high quality clinical breast exams. Further, patient-performed breast self-exams are also important because patients are more familiar with their breasts than their physicians. In summary, breast self-exams, clinical breast exams, and mammography (followed by additional imaging and/or biopsy when necessary) are each important parts of the breast cancer detection process.
Argument: Mammogram technology is over 50 years old. Such an outdated technology should not be the only option to screen for breast cancer.
Rebuttal: Actually, breast x-rays have been performed since the 1920s. However, modern mammography has only existed since around 1970, when the first dedicated mammography imaging systems became widely available. Since that time, there has been tremendous advancement in the technology so that today’s mammograms differ markedly even from those of the early 1980s. In 2002, the Mammography Quality Standards Act (MQSA) regulations will require a significant number of existing mammography systems to undergo replacement or substantial upgrade in order for them to meet increasingly rigid quality standards.
Furthermore, mammography is not the only exam that should be performed to screen for breast cancer. Monthly breast-self exams and regular physician-performed clinical breast exams are equally important. However, the argument that mammography is not effective because it was originally developed many years ago is unfounded. Modern mammography has evolved into a specialized technology that uses specifically designed and manufactured x-ray tubes, targets, films, and processors. It is not coincidental that the deaths from breast cancer have declined since modern mammography was developed.
Argument: Women need an exam that will accurately detect breast cancer without exposing them to radiation or breast compression.
Rebuttal: A painless exam that could easily and accurately detect breast cancer without using radiation or breast compression would be ideal, but currently no such exam exists. Scientists, researchers and medical systems manufacturers are constantly at work, trying to develop new tests to improve and enhance the detection of breast cancer.
In the meantime, patients should be made aware that the current radiation exposure from modern mammography is not a risk, and the benefit of detecting breast cancer at an early stage with mammography far outweighs the temporary discomfort that some women experience during breast compression. Mammography cannot detect all breast cancers. However, it can detect approximately 85% of them, and at this moment, this is better than any other method available.
- To learn more about mammography, please visit http://www.imaginis.com/breasthealth/mammography.asp
- To learn more about guidelines for early breast cancer detection, please visit http://www.imaginis.com/breasthealth/earlydetection.asp
- To learn tips for choosing a state-of-the-art mammography facility, please visit http://www.imaginis.com/breasthealth/mammography_facility.asp
- To learn about common breast cancer myths (and facts about the disease), please visit http://www.imaginis.com/breasthealth/bcmyths.asp
- To learn about key steps to ensure an optimal mammogram, please visit http://www.imaginis.com/breasthealth/quality.asp
- To learn about advances in mammography and other breast imaging methods, please visit http://www.imaginis.com/breasthealth/advances.asp
- The October, 2, 2000 Imaginis report, "Controversial Study Finds Clinical Exams Equal to Mammography With Respect to Breast Cancer Mortality For Women in Their Fifties," is available at http://www.imaginis.com/breasthealth/news/news10.02.00.asp
- The November 2, 2000 Imaginis report, "Controversy Continues Over When Women Should Start Annual Mammograms," is available at http://www.imaginis.com/breasthealth/news/news11.02.00.asp
- The September 19, 2000 Imaginis report, "Breast Cancer Death Rate Drops in Britain," is available at http://www.imaginis.com/breasthealth/news/news9.19.00.asp
- The August 29, 2000 Imaginis report, "Organization Funds Research Of Early Breast Cancer Detection Methods," is available at http://www.imaginis.com/breasthealth/news/news8.29.00.asp
- The July 24, 2000 Imaginis report, "Minimizing Pain and Discomfort During Mammography," is available at http://www.imaginis.com/breasthealth/news/news7.26b.00.asp
- The June 27, 2000 Imaginis report, "Physical Breast Exams Helpful in Detecting Breast Cancer," is available at http://www.imaginis.com/breasthealth/news/news6.27b.00.asp
Updated: March 02, 2001