What are the benefits and harms for women considering a mammogram?

Bottom Line:

The paper’s authors suggest that balanced discussions about the benefits and harms of screening mammography should focus on:

  • the possibility of breast cancer deaths avoided but also
  • the possibility of false alarms and overdiagnosis (the detection of abnormalities that will never progress enough to cause symptoms or death during a patient’s lifetime).

Although some women are comfortable with a high rate of false positive results, some women will experience lasting consequences (Ann Fam Med 2013;11:106-15) and should know the risk of harm when making the decision whether to screen.

Reference:

Welch HG, Passow HJ. Quantifying the benefits and harms of screening mammography. JAMA Intern Med 2014;Dec 30. [Epub ahead of print]

Synopsis

Sometimes we forget there are harms associated with screening for disease. Though the possibility of benefit might be worth the risk of harm, this trade-off should be considered in the decision-making process. The authors of this analysis identified, in the fog of information swirling around cancer screening, 3 outcomes that should be considered:

  1. breast cancer deaths avoided,
  2. false alarms, and
  3. overdiagnosis (the diagnosis of “disease” that will never cause symptoms or death during a patient’s lifetime).

Note that no controlled research has shown decreased overall mortality as a result of screening. The authors used currently available data from trials of annual screening mammography — the most common screening practice in the United States — to give a range of estimates for these 3 outcomes for women at different ages.

  1. breast cancer death avoidance:
    • most optimistic reduction based on randomized trial data, a 36% reduction. Although some randomized studies and epidemiologic data point to no benefit, the authors chose a conservative lower estimate of a 5% reduction.
  2. false-positive rate: a) If you screen 1000 40 year old women for 10 years, 0.1 to 1.6 will avoid dying of breast cancer, 510 to 690 will have at least 1 false alarm, and 60-80 will have a biopsy that confirms a false positive mammogram.  b) Among 1,000 50-year-old women, 0.3 to 3.2 will avoid dying from breast cancer, 490 to 670 will have at least 1 false alarm, with 70 to 100 undergoing a biopsy. c) Among 1,000 60-year-old women: 0.5 to 4.9 will avoid dying from breast cancer 390 to 540 will have at least 1 false alarm, with 50 to 70 undergoing a biopsy
  3. Over-diagnosis: a) Of those 1,000 40-year-old women, up to 11 will be over-diagnosed and treated without the possibility of benefit.  b) Of those 1000 50 year old women, 3 to 14 will be over-diagnosed and treated without the possibility of benefit. c) Among 1,000 60-year-old women, 6 to 20 will be over-diagnosed and treated without the possibility of benefit

This post was modified from the original post by Allen F. Shaughnessy, PharmD, MMedEd, Professor of Family Medicine, Tufts University, Boston, MA

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