MAMMOGRAPHY DATA

Quantifying the Benefits and Harms of Screening Mammography

Welch HG, Passow HJ
JAMA Intern Med. 2013 Dec 30. [Epub ahead of print]

Study Summary

Screening mammography offers the potential to avoid breast cancer but also carries with it the risk for false-positive results, over diagnosis of breast cancer, and unnecessary treatment. Welch and Passow sought to quantify the risks and the benefits of screening mammography so that they could be shared with women to help them make informed decisions.

Three outcomes related to screening mammography are quantified for women with mammography beginning at age 40, 50, and 60 years: (1) reduction in breast cancer deaths; (2) false-positive results (including subsequent biopsies); and (3) over diagnosis. These outcomes are reported in terms of 1000 women screened yearly for a period of 10 years. Because of variability, statistical uncertainty, as well as heterogeneity of the populations studied, results are given in a range of the upper and lower limits for each outcome.

For each outcome, a chart is provided to show how the data were obtained from randomized trials of screening mammography. For the reduction in breast cancer deaths, the death rate measurement was carried out 5 years beyond the 10-year measurement, on the basis of the presumption that 10 years of screening results in a mortality reduction that extends to 15 years. False-positive outcomes were classified as either a recall for additional testing or a biopsy recommendation.

These are the results for the individual age groups:

Among 1000 women, 40 years of age, undergoing annual mammography for 10 years:

• Between 1 and 16 women will avoid dying of breast cancer;

• Between 510 and 690 will have at least 1 false-positive test, with 60-80 undergoing biopsy; and

• Up to 11 women will be over diagnosed and treated needlessly with surgery, radiation, or chemotherapy. (No data were available to determine the lower end of over diagnosis with mammography starting at 40 years of age.)

Among 1000 women, 50 years of age, undergoing annual mammography for 10 years:

• Between 3 and 32 women will avoid dying of breast cancer;

• Between 490 and 670 will have at least 1 false-positive test, with 70-100 undergoing biopsy; and

• Between 3 and 14 will be over diagnosed and treated needlessly with surgery, radiation, or chemotherapy.

Among 1000 women, 60 years of age, undergoing annual mammography for 10 years:

• Between 5 and 49 women will avoid dying of breast cancer;

• Between 390 and 540 will have at least 1 false-positive test, with 50-70 undergoing biopsy; and

• Between 6 and 20 will be over diagnosed and treated needlessly with surgery, radiation, or chemotherapy.