Position
The scientific evidence from randomized trials on the impact of screening mammography in saving lives is conflicted, and the quality of the individual trials limited. The National Breast Cancer Coalition Fund (NBCCF) believes, on the basis of recently published reviews, that the benefits of screening mammography in reducing mortality are modest and there are harms associated with screening. No individual woman can be assured that screening mammography will be effective for her, and from a public health perspective, the harms and public health costs of screening mammography may outweigh the modest benefits of the intervention. Mammography does not prevent or cure breast cancer, and has many limitations. Therefore, a woman's decision to undergo a screening mammogram must be made on an individual level, based on quality information about her specific risk factors, and her personal preferences. Women who have symptoms of breast cancer such as a lump, pain or nipple discharge should seek a diagnostic mammogram. Ultimately, resources must be devoted to finding effective preventions and treatments for breast cancer and tools that detect breast cancer truly early.

What is a Mammogram?
A mammogram is an x-ray of the breast that can reveal abnormalities (benign or malignant). The procedure involves compressing the breast between two plates and then applying a small dose of radiation to produce an x-ray image. Mammograms can be used for screening and for diagnosis.

 

• Diagnostic Mammogram - is performed to help detect breast cancer if a woman has symptoms, such as a lump that can be felt in her breast.

 

 

• Screening Mammogram - is performed to attempt to detect breast cancer before symptoms occur. The goal of screening mammography programs is to decrease mortality from breast cancer.

 

Research on Mammography Screening
Well-designed and conducted randomized trials are the most reliable way to assess the effectiveness of any medical intervention. In the case of screening for breast cancer, the goal is to decrease the death rate from the disease and, therefore, mortality is the most reliable outcome. (For more information on the different types of outcome measures used in clinical trials, see NBCCF's fact sheet "Outcomes in Breast Cancer Clinical Trials.")

Mammography Screening Studies
There are seven published randomized trials that looked at the benefits of screening mammography for survival. 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 (1963) - enrolled 60,495 women ages 40-64
• The Malmo trial (1976) - enrolled 42,283 women ages 45-69
• The Two-County trial (1977) - enrolled 133,065 women over age 40
• The Edinburgh trial (1978) - enrolled 44,268 women ages 45-64
• The Canadian trial (parts 1 and 2; 1980) - enrolled 89,835 women ages 40-59
• The Stockholm trial (1981) - enrolled 60,117 women ages 40-64
• The Goteborg trial (1982) - enrolled 49,924 women ages 39-59

These seven trials included few women over the age of 70 and very few women of color. None of the trials examined women younger than 39 years old, and only one trial -- the Canadian trial (part 1) -- was specifically designed to examine mammography in women ages 40 to 49 years.

Analyses of the Mammography Screening Studies
The studies listed above have been subject to meta-analyses and systematic reviews by the research community.¹ NBCCF believes that the most thorough evaluations to date have been conducted by researchers affiliated with the Cochrane Collaboration (Drs. Olsen and Gotzsche in 2002, and Gotzsche and Nielsen in 2006), by Drs. Humphrey, Helfand, Chan and Woolf in 2002 for the U.S. Preventive Services Task Force (USPSTF) and by Dr. Armstrong, et al. in 2007 for the American College of Physicians. ^2-4 These scientists reviewed and evaluated the evidence on benefits and harms of mammography screening and assessed the quality of the trials.

 

• 2006 Cochrane Review
  The 2006 Cochrane review by Gotzsche and Nielsen incorporated new data since the 2002 Cochrane review and reassessed screening mammography's effect on mortality and morbidity. Using standard criteria, the researchers rated the quality of each trial's randomization methods as either adequate or suboptimal.⁵ The review included the Malmo, Canadian, New York, Two-County, Stockholm, and Goteborg trials. The Edinburgh trial was deemed biased and not included in the 2006 review.

   

  The Gotzsche and Nielsen review concluded that only two of the trials were adequately randomized - the Malmo and Canadian trials - and these trials *did not* show that mammography screening decreased mortality from breast cancer. In these trials, the women who were offered mammography screening had the same breast cancer mortality (death rate) as the women who were not offered mammography screening. In contrast, the Goteborg, New York, Stockholm, and Two-County trials, which had suboptimal randomization according to the researchers, found that mammography *did* benefit women and reduced breast cancer mortality by about 25%, on average, after 13 years.

  The researchers then calculated an overall effect on mortality by taking into account the quality of all but the Edinburgh trial. They concluded that mammography decreases the risk of death from breast cancer by about 15% in relative terms, or 0.05% in absolute terms. This means that throughout a ten-year period, 2000 women need to get screened to prevent one death from breast cancer.⁶ Of note is the fact that the methodology to estimate the overall reduction of 15% was not disclosed.

  Finally, Gotzsche and Nielsen found that mammography screening leads to more false-positives, more unnecessary surgeries, and more use of aggressive breast cancer treatments. They concluded that mammography screening increased the relative risk of overdiagnosis and overtreatment by 30%. This translates to an absolute risk increase of 0.5%; which means that throughout a ten-year period, for every 2000 women screened, ten healthy women will undergo unnecessary diagnostic procedures and treatment.

   

• 2002 Review by Humphrey, et al
  Similar to the Cochrane reviews, Dr. Humphrey and colleagues produced a summary review of the most up to date results from the seven trials for the USPSTF. Their analysis deemed the Canadian trial as fair or better quality, the New York, Goteborg, Stockholm, Malmo and Two-County trials as fair quality, and the Edinburgh trial as poor quality (the Edinburgh trial was not included in their analysis). In their review, they conclude that screening mammography significantly reduced the risk of breast cancer mortality in screened women compared with unscreened women by 16%. (Note that this conclusion is very similar to the 15% reached by Gotzsche and Nielsen in 2006.)

   

  For women between the ages of 40-49 years, they found a 15% relative reduction in risk associated with screening mammography. This means that throughout a fourteen-year period, 1792 women in their 40s need to get screened to prevent one death from breast cancer. However, this finding had only borderline statistical significance (RR=0.85 (CI: 0.73-0.99)).

  The Humphrey review concluded that "the absolute benefit of mammography screening on mortality is very small, and that biases in the trials could either erase or create it." Furthermore, they state: "even in the best screening settings, most deaths from breast cancer are not currently prevented."

 

• 2006 Systematic Review by Armstrong, et al.
  This review for the American College of Physicians focused on screening mammography in women 40-49 years of age. It included publications from the original mammography trials as well as 117 other studies. The reviewers indicate that studies have estimated a 7% to 23% reduction in breast cancer mortality rates with screening mammography in women in this age group. They also point to rates of false-positive results as high as 20% to 56% after 10 mammograms with consequent increases in unnecessary procedures and breast cancer-related anxiety; as well as discomfort at the time of screening and exposure to low-dose radiation. They conclude that the evidence suggests that more women in the 40-49 years age range have risks that outweigh the benefits of screening mammography. Subsequently, the American College of Physicians issued detailed guidelines for screening mammography among younger women that encourage doctors to carefully assess an individual woman's risks for breast cancer, and to discuss with them the potential benefits and harms of screening mammography in order to make informed individual decisions about screening.⁷

   

Limitations and Potential Harms of Mammography Screening
Screening mammography can produce inaccurate results, and as a result, many women receive false-positive or false-negative results. A false-positive result occurs when a mammogram shows a suspicious image, but there is actually no breast cancer. A false-negative result occurs when a woman's mammography results are normal, but she actually has breast cancer. In the United States, it has been estimated that a woman's cumulative risk for a false-positive result after ten mammograms is almost 50% and the risk for undergoing an unnecessary biopsy is almost 20%.⁸ Although biopsies are relatively simple surgeries, they can cause distress, scarring and disfigurement, and add to health care costs.

Another related potential harm of screening is overtreatment. There is a growing body of evidence that breast cancer is not one, but several diseases. Clinicians and researchers believe that some breast cancers will never spread to other parts of the body. Detecting and removing breast cancers that would never have spread to other parts of the body does not save any lives. This is an active area of research, but unfortunately, scientists have not figured out which breast cancers will eventually spread and which will not.

Mammography and Quality of Care
Women at risk for breast cancer who decide to participate in screening programs must have access to high-quality mammography. Qualified staff must perform the mammogram, and all equipment must comply with the standards set out in the Mammography Quality Standards Act (MQSA).⁹

Women receiving a mammogram should be treated with respect throughout the process. Some women experience more discomfort than others, therefore, health care providers should make every effort to reduce discomfort. Results of mammograms should be provided within 30 business days as required by the MQSA. The FDA has interpreted MQSA to require mammogram results that are *positive or suspicious* to be reported to the referring physician and/or the patient as soon as possible. Although it is impossible to establish a precise time frame, we believe that such communication should be accomplished within five business days.

Most importantly, women who get mammography screening must have access to treatment. No detection method will save lives unless followed by appropriate treatment.

Conclusion
Evidence from studies of varied quality indicate that, overall, mammography screening has a modest effect on breast cancer mortality. When analyzed in absolute terms, the death rate is reduced by just 0.05%. Like with all medical interventions, there are harms associated with screening mammography such as misdiagnosis and overtreatment. Two comprehensive reviews of the evidence conclude that the overall impact in mortality is small and biases in the trials could either "erase or create it." Women should discuss with their doctors their own risk profile, the potential benefits, harms, and complexities of screening mammography, and make informed decisions about screening. Mammography may provide benefits for some women, but it may also harm others.

NBCCF embraces a philosophy of evidence-based healtb care, and has long raised questions about the value of mammography screening and other tests. This is important because patients need to be assured about the value of all medical interventions, and public health resources need to be used with certainty about value to the public's health.

NBCCF believes that in order to make true progress in breast cancer we need to better understand what causes this disease, what puts individual women at risk beyond the known risk factors, how different types of breast cancer behave, and which treatments are appropriate and effective for each type of breast cancer to ensure that women receive quality care. With that knowledge, and with improved screening methodologies, we could target screening to those who would truly benefit from it.

Women need to know the truth about mammography screening, including its potential benefits, harms, and limitations. As breast cancer activists, NBCCF welcomes discussion of the effectiveness of all breast cancer interventions. We must recognize 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 these answers.

About NBCCF
The National Breast Cancer Coalition Fund 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.

Footnotes

¹ In both a systematic review and meta-analysis, results from individual published research studies are pooled together and their collective findings summarized. In general, a good systematic review or meta-analysis is a better guide to assess the benefits of an intervention than an individual article.

² Gotzsche PC, Nielsen M. Screening for breast cancer with mammography. Cochrane Database of Systematic Reviews 2006, Issue 4. Art. No.: CD001877. DOI: 10.1002/14651858.CD001877.pub2.

³ Humphrey LL, Helfand M, Chan BK, et al. Breast cancer screening: a summary of the evidence for the U.S. Preventive Services Task Force. Ann Intern Med. 2002 Sep 3; 137(5 Part 1):347-60.

⁴ Armstrong K, Moye E, Williams S, Berlin JA, Reynolds EE. Screening mammography in women 40 to 49 years of age: a systematic review for the American College of Physicians. Ann Intern Med 2007 Apr 3; 146(7): 516-26.

⁵ Each trial was classified based on the likelihood that its randomization methods may have led to selection bias. Selection bias is an error in selecting a study group (or groups) within a study and can have a major impact on the validity of the study and the legitimacy of its conclusion.

⁶ Absolute risk reduction is the difference in breast cancer mortality between the screened group and control group. For example, when assessing the benefit of screening mammography on breast cancer mortality, if 2% of patients die from breast cancer within the control group (those not being screened) compared to 1.5% of patients within the screened group, then the absolute risk reduction would be 0.5% (2% - 1.5% = 0.5%).

⁷ Qaseem A, Snow V, Sherif K, et al. Screening mammography for women 40 to 49 years of age: a clinical practice guideline from the American College of Physicians. Ann Intern Med 2007; 146: 511-15.

⁸ Elmore JG, Barton MB, Moceri VM, Polk S, Arena PJ, Fletcher SW. Ten-year risk of false positive screening mammograms and clinical breast examinations. N Engl J Med 1998 Apr 16; 338(16): 1089-96.

⁹ Congress enacted the Mammography Quality Standards Act (MQSA) in 1992 to ensure that all women have access to quality mammography. In the fall of 2004, Congress reauthorized MQSA, extending the program to 2007. Under this act, The Food and Drug Administration (FDA) is responsible for developing, implementing, and enforcing quality standards for mammography.