Sunday, February 17, 2013

Shared decisions in screening for breast cancer

- Kenny Lin, MD

In the February 15th issue of AFP, Dr. Maria Tirona reviews areas of agreement and disagreement in major organizational guidelines on screening for breast cancer. There is widespread consensus that annual or biennial mammography should be offered to women 50 to 74 years of age, and that teaching breast self-examination does not improve health outcomes. For women 40 to 49 years of age, in whom the risks and benefits of mammography are closely balanced on a population level, the U.S. Preventive Services Task Force and the American Academy of Family Physicians recommend shared decision making, taking into account individual patient risk and patients' values regarding benefits and harms of screening.

In an accompanying editorial, however, Drs. Russell Harris and Linda Kinsinger argue that shared decision making regarding breast cancer screening need not be limited to younger women:

More and more, the goal for breast cancer screening is not to maximize the number of women who have mammography, but to help women make informed decisions about screening, even if that means that some women decide not to be screened. ... The goal of improving patient decision making should be expanded to all women eligible for breast cancer screening (i.e., those 40 to 75 years of age who are in reasonable health), because the benefits and harms of screening are not very different among these age groups.

The primary benefit of screening mammography is an estimated 15 percent relative reduction in deaths from breast cancer; harms of mammography include false positive results, overdiagnosis, and overtreatment. A recent study published in BMJ explored the impact of overdiagnosis on attitudes toward mammography in several focus groups of Australian women 40 to 79 years of age. Few women had ever been informed about overdiagnosis as a potential harm of screening. Most women continued to feel that mammography was worthwhile if overdiagnosis was relatively uncommon (30 percent or less of all breast cancers detected). However, a higher estimate of overdiagnosis (50 percent) "made some women perceive a need for more careful personal decision making about screening."

Notably, a 2011 Cochrane Review estimated that 30 percent of breast cancers detected through screening are overdiagnosed:

This means that for every 2,000 women invited for screening over 10 years, one will have her life prolonged, and 10 healthy women who would not have been diagnosed if there had not been screening will be treated unnecessarily. Furthermore, more than 200 women will experience important psychological distress for many months because of false-positive findings.

Given this information, what approach do you take to screening mammography? Do you believe that this test should be routine for women of eligible ages, a shared decision for some, or (as Drs. Harris and Kinsinger advocate), a shared decision for all? Why is it often difficult to promote shared decision making in clinical practice?

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