Organized Breast Cancer Screening Programs in Canada - 1996 Report

Results of Screening

An important requirement of mammographic screening is high specificity - the probability of a negative screening result if the disease is truly absent. This minimizes the number of healthy women who are informed that their screen was abnormal and who are then subjected to further diagnostic investigations, which can cause psychological distress and financial costs to the woman and society. Figure 4 indicates that between 11% and 12.4% of first screens were reported as abnormal. For rescreens, the abnormal recall rate was much lower (5.1% to 5.7%). The abnormal recall rate differed little among age groups.

The rate of abnormal screens was slightly higher for first screens in comparison with standards set by other national breast screening programs (see Table 3), which specify that less than 7-10% of first screens should be abnormal. However, these programs use mammography as the sole modality of screening, whereas several Canadian programs also use clinical breast examination. Table 6 shows that, with the exception of women under 50, the use of clinical breast examination accounted for approximately one fifth of the abnormal screens. For those over 50 years of age, the rates of abnormalities detected by mammography only are in line with the standards set by the U.K. and the Australian breast screening programs.

Figure 4 Abnornal recall rate* by age group, 1996

* Includes mammography and clinical breast examination as screening modalities.

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