Canadian National Breast Screening Study
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The Canadian National Breast Screening Study, sometimes abbreviated as CNBSS or NBSS, was a randomized trial conducted with the aim of evaluating whether mammography reduced breast cancer incidence or mortality among women who underwent screening.[1] The trial was initiated in 1980, and was conducted in fifteen screening centers in six different Canadian provinces.[1] It was the first study designed to determine whether mammography was effective among women between the ages of 40 and 49.[2]
In the CNBSS, nearly 90,000 women were randomly assigned to either undergo mammographic screening annually, or not undergo it, for five years (1980-1985).[3][4] The women who participated in the study were aged 40–59, and were divided into two groups: the age 40-49 group and the age 50-59 group.[3] The women aged 40–49 in the mammography group also received annual breast exams, as did the women aged 50–59 in both the mammography and control groups.[3] The women aged 40–49 in the control group received only one breast exam, after which they were told to remain under the care of their family doctor.[1][3]