Women’s Health Update

by Tori Hudson, ND

Screening Mammography:

An

Update

on

the

Controversy

Not long ago, I read an editorial in the New England Journal of Medicine that has had a large influence on my thinking about screening mammography. I last wrote about screening mammography for the Townsend Letter in March 2010. That column was in response to the 2009 updated US Preventive Services Task Force (USPSTF) guidelines on screening mammography, which at the time created quite a controversy.¹

The key 2009 USPSTF recommendations are as follows:

• No universal screening mammography for women ages 40–49 and urging an individualized informed decision making process based on specific benefits and harms.

• Biennial screening mammography for women ages 50–69.

• Extend screening to women in the 70–74 year old group.

• Insufficient evidence to assess the benefits and harms of screening mammography in women 75 and older.

• Insufficient evidence to assess the benefits and risks of clinical breast exams in women aged 40 years and older that undergo mammography, digital mammography, and MRI versus film mammography.

• Teaching self-examination is harmful and not recommended.

• These recommendations do not apply to women who are at excess risk for breast cancer due to known genetic mutations or histories of chest radiation.

Studies and commentaries have continued to be published as to the value of mammography in reducing breast cancer mortality, and we won’t review all of them here, but rather give you some key concepts that I gleaned from the insightful editorial from the NEJM.² More than 600,000 women have participated in 10 randomized trials of approximately 10 years of follow-up. It appears to be the most carefully studied screening test of all; yet, despite this, it continues to be one of the most controversial in terms of relative merit and the balance of benefit and harm – “harm” in this case refers to unnecessary biopsies, not radiation exposure.

In a study reported in that same issue of the NEJM, Norwegian researchers provided data that stated that the benefit of screening mammography is modest in the national screening program of Norway.³ The conclusions reported that the benefit of the Norwegian screening program was “disappointingly small: a 10% reduction in breast-cancer mortality among women between the ages of 50 and 69 years.” They also go on to say that this 10% reduction in mortality was due to not only screening mammography but multidisciplinary teams instituted to better treat breast cancer. They asserted that the latter was the more important of the two factors, given that the women over age 70 were only exposed to the multidisciplinary treatment teams and not screening mammography and had an 8% relative reduction in mortality. “Thus, the relative reduction in mortality due to screening mammography alone could be as low as 2%.”

This 10% relative reduction reported in the Norwegian study is much smaller than the 15% to 23% estimated mortality reduction reported by the USPSTF. One explanation could be that the task force reported on randomized trials and the Norwegian data are observational. Concerns could be considered, but the authors agreed that effects of differences among the four study groups, contamination, and perhaps a too short follow-up period were small and not a good explanation for this low number of 10%. The other explanation is fascinating to me in that the NEJM editor asserts that both the task force and the Norwegian researchers are correct. He states that the randomized trials reflect the world before 1990 and the observational data reflect the world after 1990. He goes on to say that “it is quite plausible that screening mammography was more effective in the past than it is now. If women with new breast lumps now present earlier for evaluation, the benefit of screening will be less. If treatment of clinically detected breast cancer-(i.e. tumors that are detected by means other than screening) has now improved, the benefit of screening will be less. Thus, the increased awareness about the importance of promptly seeking care for overt breast abnormalities and the widespread use of adjuvant therapy have probably combined to make screening now less important.”^4,5

Let’s assume for a moment that mammography screening is associated with a 10% reduction in the rate of death from breast cancer and that all the benefit comes from screening mammography, not treatment. That would mean that the 10-year risk of breast-cancer death for a 50-year-old US woman is about 4 per 1000. If the risk already incorporates the benefit of screening mammography, the risk estimate without screening mammography would be approximately 4.4 per 1000. Another way of putting this is that with the addition of screening mammography, the number of women who will not die from breast cancer goes from 995.6 to 996 per 1000 women, making the absolute benefit 0.4 per 1000 women. This translates to 2500 women would need to be screened annually over a 10-year period for 1 to avoid death from breast cancer. That means that 2499 women had to undergo screening mammography to achieve this benefit. It is estimated that more than 1000 women in the US would have at least one false positive result, although this would be considerably lower in Europe. Overdiagnosis is a greater problem, and between 5 and 15 women would undergo unnecessary treatment.

A new analysis of breast cancer screening in European countries was also just

published and suggested that screening had little effect on breast cancer mortality.⁶ In another recent publication of Swedish data based on 3 decades of follow-up, major benefits of screening were observed with a 31% lowered risk of breast cancer mortality in the screening group, but it is still important to note that the number of women needed to screen for 7 years to prevent 1 breast cancer death as 414.⁷

Some readers of this column will conclude that they won’t recommend screening mammography at all. I do not conclude that but rather have an increased awareness that the mortality benefit is possibly modest and that my recommendations and my patient’s decision is may in fact be a close call, with trade-offs of modest benefit and modest harm. This highlights the need for us to make individual recommendations based on known risk factors of obesity, more than 7 alcohol drinks per day, first-degree relative with breast cancer history, and BRCA mutations. I no longer recommend routine screening mammography in low-risk women aged 40 through 49. I typically recommend biannual screening or even the more European trend of every 3 years for low-risk women ages 50 through 69, and annual screening for higher-risk women 40 and older. I always try to present my recommendations in a manner that provides them with information and encouragement to decide what they are comfortable with and what choice they want to make for themselves. These now informed individuals are left to make their own decisions.

Notes

1. Mandelblatt J et al. Effects of mammography screening under different screening schedules: Model estimates of potential benefits and harms. Ann Intern Med. 2009;151:738–747.

2. Welch G. Screening mammography– a long run for a short slide? N Engl J Med. 2010;363;13:1276–1278.

3. Kalager M, Zelen M, Langmark F, Adami H. Effect of screening mammography on breast-cancer mortality in Norway. N Engl J Med. 2010;363:1203–1210.

4. Rostgaard K, Vaeth M, Rootzen H, Lynge E. Why did the breast cancer lymph node status distribution improve in Denmark in the pore-mammography screening period of 1978–1994? Acta Oncol. 2010;49:313–321.

5. Early Breast Cancer Trialists’ Collaborative Group. Effects of chemotherapy and hormonal therapy for early breast cancer on recurrence and 15-year survival: an overview of the randomised trials. Lancet. 2005;365:1687–1717.

6. Autier P et al. Breast cancer mortality in neighboring European countries with different levels of screening but similar access to treatment: Trend analysis of WHO mortality database. BMJ. 2011 July 28;343:d4411.

7. Tabar L et al. Swedish Two-County Trial: Impact of mammographic screening on breast cancer mortality during 3 decades. Radiology. 2011 Sep;260:658.

Dr. Tori Hudson graduated from the National College of Naturopathic Medicine (NCNM) in 1984 and has served the college in many capacities over the last 25 years. She is currently a clinical professor at NCNM and Bastyr University; has been in practice for 25 years; and is the medical director of the clinic A Woman’s Time in Portland, OR, and director of research and development for Vitanica, a supplement company for women. She is also a nationally recognized author, speaker, educator, researcher, and clinician.