Mammography Screening Trial Update

ACR Statement on Landmark Mammography Screening Trial

A landmark paper published in the July 2011 issue of Radiology, one of the leading journals for medical imaging, should put an end to the controversies over the effectiveness of mammography screening.

The study, known as the Two County Trial in Sweden, is a randomized, controlled trial (RCT), one of the most rigorous types of scientific studies available to evaluate the efficacy of medical tests. The 29-year follow-up is the longest for any mammography RCT. More than 130,000 women from 40 to 74 years of age were included in the trial. Roughly half were screened over a seven year period.

Essentially, the trial compared the death rate from breast cancer from two randomly assigned groups of women: women who were invited to be screened with mammography alone, compared with a control group of women who were not invited to be screened at all. About 85% of the women invited were actually screened. The death rate was 30 percent lower among the women invited to be screened.

This latest paper not only confirms that screening with mammography alone can save thousands of lives, but furthermore, the mortality benefit continues over time. More than half of the cancer deaths in this study occurred more than 10 years after screening began, demonstrating an enduring effect for almost three decades.

The Two County Trial screened women in their forties about every 24 months, and women aged 50-74 about every 33 months. The mammograms were obtained using only a single view of each breast. If the American Cancer Society recommendations were to be followed (screening annually starting at age 40), with two views of each breast, the number of lives saved is likely to be higher than was seen in this trial. For women who actually participate in screening, the benefit is likely to be even higher. 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 each year.

In contrast, the US Preventive Services Task Force (USPSTF) issued guidelines in 2009 suggesting that women need not begin screening until the age of 50. They used an estimate of only a 15 percent decrease in breast cancer deaths in their calculations. Had they used the estimate of 30 percent, they may have reached different conclusions and made different recommendations. Furthermore, the estimate of the “number needed to screen” to save a life (NNS) from this latest study is far more accurate, and much lower, than that estimated by the USPSTF for women under the age of 60 years.

The USPSTF should withdraw its 2009 guidelines and support annual screening, beginning at the age of 40, for all women. Physicians who have been asked by the USPSTF to discuss screening with each of their younger patients would be wise to consider the results of this important screening trial.

While treatment for breast cancer has improved over the years, early detection with mammography is crucial to better results. Mammography screening is clearly the main reason that deaths from breast cancer have decreased in the United States since 1990.

To speak with an ACR spokesperson, please contact Shawn Farley at 703.648.8936 or PR@acr.org.