June 28, 2011
Commentary on the latest Swedish Two-County Trial Report by Daniel B. Kopans, MD Swedish Two-County Trial: Impact of Mammographic Screening on Breast Cancer Mortality during 3 Decades. Tabar L, Vitak B, Chen THH, et al. Radiology 2011; pre-release (ahead of print publication)
View the original commentary here on SBI's Web site
"Mammography screening is one of the major medical advances of the last 50 years. The death rate from breast cancer had been unchanged for at least 50 years. Mammography screening began at a national level in the U.S. in the mid-1980’s, and, as would be expected, the death rate began to decline in 1990. Since then the death rate has decreased by over 30%. Therapy has helped to reduce deaths, but therapy only saves lives when cancers are found early. Data from the Netherlands and Sweden have clearly shown that it is screening that accounts for most of the decrease in deaths. The major impact of screening has been lost by the numerous controversies that have swirled around mammography. For many years the debate centered on whether or not screening could save lives. Once this became apparent (although there continue to be those who doubt the clear scientific evidence), the debate has been over whether or not there is benefit from screening women ages 40-49. Following the first randomized, controlled trial of breast cancer screening performed within the Health Insurance Plan of New York (HIP) in the 1960’s, a large study was undertaken in Sweden that involved women in two counties and has been named the Two County Trial. Over 130,000 women were involved in the trial. A little more than half of the women were invited to be screened while the other half were not invited, but got the standard health care at the time. This trial was designed to see if high quality mammography screening alone, without clinical breast examination (CBE), could reduce deaths from breast cancer. The first publication from the Two County trial in the mid-1980’s clearly showed a decrease in deaths for screening from age 40-74, and this resulted in the start of screening in the U.S. and around the World.
This latest paper with 29 years of follow-up of the Two County Trial not only confirms the fact that screening with mammography, alone, can save thousands of lives, but it also shows that the benefit continued even after the screening ended. Fortunately, most breast cancers do not kill women quickly. The very fast growing cancers, unfortunately, are not often detected by screening periodically, and many of these are not detected early enough to save lives. However, there are many cancers that, if not found early enough will, ultimately kill women 5, 10, or more years after diagnosis. These are the cancers which, if found early, can prevent a woman from dying later in life. This recent study from the Two County Trial clearly shows that these are the lives that are being saved by screening. Even though many women die from their breast cancers years after their cancers are diagnosed, screening prevents many of these deaths and even 20 years after screening fewer women die in the screened group. The benefit of screening, in preventing these deaths is clear, and it is also clear that the benefit came from screening women beginning at the age of 40. Mammography screening is not perfect. It does not find all cancers and does not lead to a cure for all women, but screening beginning at the age of 40 saves thousands of lives.
The United States Preventive Services Task Force, unfortunately, caused a great deal of confusion by suggesting that women did not need to be screened until the age of 50. It is now clear that this would result in tens of thousands of deaths that could be prevented by annual screening beginning at the age of 40. This latest paper again confirms the value of screening beginning at the age of 40.
With regard to the “number needed to screen” to save a life (NNTS). This was raised by the US Preventive Services Task Force because they were prohibited, by their charter, from doing “cost/benefit” analysis. It was a way for them to suggest that screening younger women was not worth the cost. An individual woman gets screened only once a year so that the NNTS is fairly meaningless to her. Adding insult to injury, the USPSTF used the wrong data to determine NNTS. They used numbers for the randomized, controlled trials which were actually the number of women needed to be invited to be screened (many refused the invitation). This latest study provides the actual number of women needed to be screened and is far more accurate and smaller than that used by the USPSTF.
The USPSTF clearly based their guidelines on scientifically unsupportable analyses. They should, once more, support annual screening beginning at the age of 40."
Daniel B. Kopans, M.D. Professor of Radiology, Harvard Medical School
Senior Radiologist, Breast Imaging Division
Department of Radiology, Massachusetts General Hospital
Avon Comprehensive Breast Evaluation Center
ACC Suite 240
15 Parkman Street
Boston, MA 02114