Should women undergo mammograms? YES.By Jae Hong Lee, MD, MPH
For many years, women have been told that regularly scheduled mammograms can help detect breast cancer early and save lives, reducing the number of deaths from breast cancer. In recent months, there have been many reports in newspapers and on television questioning the value of mammograms. These reports focused primarily on a recent study by two Danish scientists claiming to show evidence that using mammograms to screen for breast cancer does not save lives.1, 2 This has led to much confusion among physicians and their patients. Many women are asking whether they should continue undergoing regularly scheduled mammograms. We say the answer to that question is YES.
First, it is important to know what studies have been done on the impact of mammograms in saving 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 reductions in the number of breast cancer deaths ranging from 13 to 45%.3-8 Only one large study, performed in Canada, has shown no difference in the number of breast cancer deaths with the use of mammograms.9-11 Some scientists have criticized the design of the Canadian study because it compared mammography plus physical examinations 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.12 Since many women have mammograms instead of physical exams, these study results are misleading. There are other studies showing 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.13 That last point is important, because even if the new Danish study is correct and mammograms do not save lives, earlier detection combined with less extensive surgery would be a significant quality-of-life benefit.14 Finally, years of experience have proven mammography to be a safe and reliable procedure, as long as mammograms are performed in accordance with federal regulations (as outlined under the Mammography Quality Standards Act15).
So what is this new study that is causing the recent controversy? The authors of that 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 7 large clinical studies mentioned above. Meta-analyses are becoming 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 some software. However, performing a meta-analysis also requires many subjective decisions by the scientists that can bias the results. For example, many scientists 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.16, 17 Many researchers would 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.
So why all the fuss over a small study with no new data produced by just two Danish scientists? First, the Danish study was published in a prestigious British medical journal, The Lancet. Publication in such a journal tends to lend weight to a scientific report, but that does not guarantee the quality or true importance of the study. Second, it is likely that some journalists could not critically evaluate the type of study whose results they were reporting. 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 has overemphasized the importance of the Danish study, leading to confusion among thousands of patients around the world.
Although the importance of the Danish study may have been overemphasized, the authors did discuss important potential problems with breast cancer screening using mammograms: unnecessary biopsies or overaggressive treatment.1, 2 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.18 Overly aggressive treatment is also a well-documented problem, and not only because of mammograms. Many breast cancer patients, for example, undergo mastectomies when they are eligible for less extensive breast-conserving surgery.19-21 While it is important for women to continue undergoing regularly-scheduled mammograms to detect breast cancer early, it is just as important for women 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.
In summary, the recent Danish study is just one small part of the vast medical literature studying the value of mammograms. The data currently available strongly support the benefits of using mammograms to screen for breast cancer-- including earlier detection and fewer breast cancer deaths. Unless new original data from a large clinical study suggest otherwise, women should ignore the current hullabaloo and continue to undergo regularly-scheduled mammograms.
References:1. Gotzsche PC, Olsen O. Is screening for breast cancer with mammography justifiable? Lancet. Jan 8 2000;355(9198):129-134.
2. Olsen O, Gotzsche PC. Cochrane Review on Screening for Breast Cancer with Mammography. Lancet. 2001;358:1340-1342.
3. Andersson I, Janzon L. Reduced breast cancer mortality in women under age 50: updated results from the Malmo Mammographic Screening Program. J Natl Cancer Inst Monogr. 1997(22):63-67.
4. Alexander FE, Anderson TJ, Brown HK, et al. 14 years of follow-up from the Edinburgh randomised trial of breast-cancer screening. Lancet. Jun 5 1999;353(9168):1903-1908.
5. Bjurstam N, Bjorneld L, Duffy SW, et al. The Gothenburg breast screening trial: first results on mortality, incidence, and mode of detection for women ages 39-49 years at randomization. Cancer. Dec 1 1997;80(11):2091-2099.
6. Chu KC, Smart CR, Tarone RE. Analysis of breast cancer mortality and stage distribution by age for the Health Insurance Plan clinical trial. J Natl Cancer Inst. Sep 21 1988;80(14):1125-1132.
7. Frisell J, Lidbrink E, Hellstrom L, Rutqvist LE. Followup after 11 years--update of mortality results in the Stockholm mammographic screening trial. Breast Cancer Res Treat. Sep 1997;45(3):263-270.
8. Tabar L, Fagerberg G, Chen HH, et al. Efficacy of breast cancer screening by age. New results from the Swedish Two-County Trial. Cancer. May 15 1995;75(10):2507-2517.
9. Miller AB, To T, Baines CJ, Wall C. The Canadian National Breast Screening Study: update on breast cancer mortality. J Natl Cancer Inst Monogr. 1997(22):37-41.
10. Miller AB, Baines CJ, To T, Wall C. Canadian National Breast Screening Study: 2. Breast cancer detection and death rates among women aged 50 to 59 years. Cmaj. Nov 15 1992;147(10):1477-1488.
11. Miller AB, Baines CJ, To T, Wall C. Canadian National Breast Screening Study: 1. Breast cancer detection and death rates among women aged 40 to 49 years. Cmaj. Nov 15 1992;147(10):1459-1476.
12. Law M, Hackshaw A, Wald N. Screening mammography re-evaluated. Lancet. Feb 26 2000;355(9205):749-750; discussion 752.
13. Solin LJ, Legorreta A, Schultz DJ, Zatz S, Goodman RL. The importance of mammographic screening relative to the treatment of women with carcinoma of the breast. Arch Intern Med. Apr 11 1994;154(7):745-752.
14. Lee JH, Zuckerman D. Screening for breast cancer with mammography. Lancet. Dec 22-29 2001;358(9299):2164-2165.
15. Monsees BS. The Mammography Quality Standards Act. An overview of the regulations and guidance. Radiol Clin North Am. Jul 2000;38(4):759-772.
16. Duffy SW, Tabar L. Screening mammography re-evaluated. Lancet. Feb 26 2000;355(9205):747-748; discussion 752.
17. Hayes C, Fitzpatrick P, Daly L, Buttimer J. Screening mammography re-evaluated. Lancet. Feb 26 2000;355(9205):749; discussion 752.
18. Lehman CD, Miller L, Rutter CM, Tsu V. Effect of training with the American College of Radiology breast imaging reporting and data system lexicon on mammographic interpretation skills in developing countries. Acad Radiol. Jul 2001;8(7):647-650.
19. Zuckerman DM. The need to improve informed consent for breast cancer patients. J Am Med Womens Assoc. Fall 2000;55(5):285-289.
20. Dolan JT, Granchi TS. Low rate of breast conservation surgery in large urban hospital serving the medically indigent. Am J Surg. Dec 1998;176(6):520-524.
21. Kotwall CA, Covington DL, Rutledge R, Churchill MP, Meyer AA. Patient, hospital, and surgeon factors associated with breast conservation surgery. A statewide analysis in North Carolina. Ann Surg. Oct 1996;224(4):419-426; discussion 426-419.
