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.
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:
- breast cancer deaths avoided,
- false alarms, and
- 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.
- 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.
- 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
- 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