Variation of benefits and harms of breast cancer screening with age.

The critical issue in deciding whether to recommend breast cancer screening for women in their forties is to determine whether potential benefits are substantially greater than potential harms. Recent evidence from randomized clinical trials makes it likely that, after 10-12 years of follow-up, there is a real benefit from screening women ages 40-49, on the order of a 15-20% reduction in the relative risk of breast cancer death. This relative risk reduction translates into an absolute risk reduction of 1-2 women whose lives are extended from screening 1,000 women in their forties annually for 10 years (i.e., about one life extended per 5,000 mammograms). The absolute benefit of screening increases with age. Evidence about potential harms is less well established, but it is compelling that there are 15-40 times as many false positive as true positive mammograms (depending on the patient's age), and that at least some of the women with false positive mammograms have ongoing psychological distress as a result. Some 30% of all women who are screened annually during their forties will have at least one false positive mammogram and this probability likely decreases with advancing age. If the balance between benefits and harms is judged to be a "close call" for women in their forties, a blanket recommendation for all is inappropriate. Instead, each woman in her forties should be helped to understand the pros and cons of screening, to clarify her own values, and to consider with her primary care physician what decision would be best for her.