A sobering surprise: Regular mammography saves few lives

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Very few women whose breast cancer was detected by routine mammography have actually had their lives saved by the screening, conclude the authors of a study just published in the Archives of Internal Medicine. And, while the finding runs contrary to the now popular promotion of an annual mammogram, it actually accords with a number of other studies that have questioned the benefits of yearly mammogram screening. In fact, the U.S. Preventive Task Force in 2009 advised that women delay regular screening until age 50, instead of 40, as well as limiting screening to every other year, instead of annually. Such recommendations received a considerable amount of flack, however, from women who feared that skipping a yearly mammogram would increase their risk of dying from breast cancer.

But the latest study, conducted by two researchers at the Dartmouth Institute for Health Policy and Clinical Practice, aims to dispel these widespread beliefs. Using data and analytical software from the National Cancer Institute, the researchers estimated the risk of dying from breast cancer in the presence and absence of mammography in women ranging in age from 40 to 70 years. Specifically, they looked at a woman s 10-year risk of developing breast cancer and her 20-year risk of death, taking into consideration the value of detection and the benefits of improved treatments. Ultimately, they found that, among women who actually have breast cancer that was detected by screening, only 3 to 13 percent of them were actually helped by the test.

What s the reason for the surprisingly small effect of mammography on breast cancer outcomes? Lead author Dr. H. Gilbert Welch explains that the majority of cancers fall into three out of four main categories: Slow-growing, which will be found and treated regardless of screening; aggressive, which are deadly even when detected early by screening; or innocuous, which don t require treatment in the first place. Mammography offers little benefit to women in these catagories.

Finally, there is a very small proportion of women with cancers that fall into the fourth category, in which the outcomes are actually improved by mammography. These women have otherwise deadly cancers that are treatable if detected at the right moment. However, only one woman per 1,000 healthy women who are screened for breast cancer falls into this last category and will actually be helped by early detection.

Nevertheless, the medical community is not dismissing the 4,000 to 18,000 women who mammography does help each year. As we ve pointed out before, a doctor and patient should decide on the frequency of a breast cancer screening based on an understanding of the 2009 guidelines as well as the patient s individual risk factors. Dr. Susan Love, a clinical professor of surgery at the University of Los Angeles School of Medicine, also points out that scientific understanding has changed in the years since mammography screening was adopted. Accordingly, she believes that there s more to be gained, instead, from a greater focus on cancer prevention and on treatment for the most aggressive cancers.

ACSH's Dr. Gilbert Ross emphasizes that annual mammography screening should really be reserved for women whose family history and health profile puts them at risk. Because, he says, the benefits are just too small for the population at large.