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?
And there will be deaths from
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2. travel to screening and repeats
3. false positive biopsies (7%) with treatment
And earlier death due to treatment
The earlier the screening
The lesser the risk
The worse the quality of screening
The worse the quality of the biopsy reads
The more the travel
The balance changes between benefit to risk
Breast cancer screening (like any other screening test) should in my opinion be a shared decision. This is simply because only a very small minority of individuals screened will benefit - and there is potential for harm from screening. Clearly, screening IS "worth it" to the individual whose life is saved by the procedure. That said - I wonder how many women might choose NOT to be screened IF they were truly provided with informed consent including information on NNT (number-needed-to-treat) that encompasses the figures you cite above (in your 2nd-to-last paragraph) on potential harms that might arise from screening. Final Thought: Many who feel their life was "saved" by screening mammography that picked up a small "cancer" might in fact not have really been saved - as we increase our appreciation of the clinical reality that some significant percentage of breast cancers (like prostate cancers) are entities that the patient dies "with" but no "of". I'll conclude by clarifying: I am definitely NOT against screening for breast cancer. But I am against doing so without providing full information so that the patient can make HER decision as to what SHE feels is right for her.
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