Older randomized trials found that screening mammograms reduced breast cancer mortality, but they were conducted during the pre-tamoxifen era when treatment of breast cancer was less effective.
In 1980, Canadian investigators began a randomized trial of mammography and physical examination in almost 90,000 women aged 40-59 years, and they now report findings based on up to 25 years of follow-up.[1] Each woman underwent an initial clinical breast exam and then was randomly assigned either to 5 annual mammograms or to no mammography.
The mean size of cancers diagnosed in the women undergoing mammography was 1.9 cm, significantly smaller than the mean of 2.1 cm in the no-mammogram group. However, the proportion of tumors that were node positive was similar in the 2 groups.