The US Department of Health and Human Services recently recommended that women older than 40 receive mammograms regularly, but the jury is still out on the relative benefit for women younger than 50.
In February, the US Preventive Services Task Force reported that it had “fair evidence that mammography screening every 12-33 months significantly reduces mortality from breast cancer.” It said that while evidence is strongest for reductions among women aged 50 to 69, “the precise age at which the potential benefits of mammography justify the possible harms [e.g., false-positive results] is a subjective choice.” The US task force did not dismiss the potential advantage of screening for women over age 40.
The Canadian Task Force on Preventive Health Care analyzed the same studies as its US counterpart, but reached a slightly different conclusion. “Current evidence regarding the effectiveness of screening mammography does not suggest the inclusion of the manoeuvre in, or its exclusion from, the periodic health examination of women aged 40-49 years at average risk of breast cancer (grade C recommendation) [CMAJ 2001;164(4):469-76].” The conclusion? “Upon reaching the age of 40, Canadian women should be informed of the potential benefits and risks of screening mammography and assisted in deciding at what age they wish to initiate the manoeuvre.”
The next chapter will be written next year when results from a large British randomized controlled trial are published. The “Age Trial” of the UK's Coordinating Committee on Cancer Research involved the 1991 recruitment of 160 000 women aged 40-41, a third of whom were invited to have an annual screening until the calendar year of their 48th birthday. The remaining two-thirds in the control group will receive screening mammography after age 50 as part of the National Health Service Screening Program. — Steven Wharry, CMAJ