How Often Should One Screen for Breast Cancer?

Women are frequently told that mammography saves lives. But seldom the question is asked, "how often?" Researchers set out to examine how often this life-saving event occurs.

Unrealistic expectations may influence a woman's decision whether or not to participate in screening mammography. Over 90% of women think that "early detection saves lives.” Drs. John D. Keen and James E. Keen, from the John H. Stroger Jr. Hospital of Cook County (Chicago, IL, USA) and the University of Nebraska (Lincoln, USA), respectively, aimed to promote informed decision-making by calculating the age-dependent absolute benefit of screening in three traditional ways: the absolute risk reduction from repeated screening, the number of women needed to screen repeatedly to save one life, and the survival percentages with and without mammography. They also estimated the average benefit of a single mammogram. Their novel concept of life-saving proportion is also relevant to economic analyses of screening.

The investigators discovered that the life-saving benefit of mammography gradually increases with age along with the screen-free absolute death risk, which is about 1% over 15 years starting at age 55. The corresponding risk of developing breast cancer is approximately 6%. Repeated screening starting at age 50 saves about 1.8 lives over 15 years for every 1,000 women screened. The average benefit of a single screening mammogram is 0.034%; in other words, 2,970 women must be screened once to save one life. Alternatively, 23 cancers must be detected. Assuming a base case 20% relative risk reduction, the survival percentage in younger women at age 40 is 99.52% without and 99.62% with screening, meaning, that there is a 0.1% increased chance of survival with screening than without it.

According to the investigators, who published their findings in April 2009 the open access journal BMC Medical Informatics and Decision Making, "We have assumed that a 'life saved' means screening helps cure one woman with breast cancer who would otherwise have died from the disease without screening ... However, all women with breast cancer may theoretically benefit from screening mammography through slowing the disease and therefore slightly prolonging their lives. For a woman in the screening subset of mammography-detectable cancers, there is a less than 5% chance that a mammogram will save her life. By comparing mammography's life-saving absolute benefit with its expected harms, a well-informed woman along with her physician can make a reasonable decision to screen or not to screen for breast cancer."

As this research article is highly controversial, BMC Medical Informatics and Decision Making has provided two commentaries in the same issue from experts in the field. Dr. Stephen Duffy of Cancer Research UK (London) argued that direct results from empirical data might be more reliable than modeled estimates derived by combining data from disparate sources. On the other hand, Dr. Michael Retsky from the Harvard Medical School (Cambridge, MA, USA) praises this study, noting that it is a positive step in the right direction considering that too often women aged 40-49 are asked to sign informed consent for mammography without being properly informed of the potential risks.

Related Links:
John H. Stroger Jr. Hospital of Cook County
University of Nebraska