Organized Breast Cancer Screening Programs in Canada

1999 and 2000 Report

Results of Screening

Although recognizing that mammography and CBE are not perfect tests, organized programs aim to ensure that all breast cancers are identified in asymptomatic women while they minimize the number of healthy women who experience follow-up procedures. 

Abnormal recall rates on first screen are normally high, reflecting prevalent cancers among previously unscreened women. Abnormal recall rates differed little among age groups, ranging from 9.9% to 11.9% of first screens obtained with mammography (Table 4). These figures may, however, be influenced by the availability of mammography outside the programs. A proportion of the women receiving a “first” program screen will have had a mammogram before entering the program. For rescreens occurring less than 2.5 years after the previous screen, the abnormal recall rate (by any mode of detection) was substantially lower, between 5.5% and 7.0% (Table 4). The lower rate may reflect either the value of having previous comparison mammograms or the likelihood that fewer cancers would develop between screens, or both factors. The abnormal recall rates for rescreens occurring at least 2.5 years after the previous screen begin to take on the profile
of first screens, which emphasizes the benefits of returning for a subsequent screen in a timely fashion. This pattern is consistent with the results presented in the 1997 and 1998 report². 

Table 4
Abnormal recall rates by mode of detection and
age group, 1999 and 2000 screen years

^a    Independent of CBE delivery or CBE findings. 

^b    Independent of mammography delivery or mammography findings. 

^c    All provinces provide mammography; Manitoba, Ontario, Nova Scotia, Prince Edward Island, and Newfoundland also provide clinical breast examinations (CBEs). 

Programs strive to minimize the number of healthy women who experience follow-up procedures. In 1999-2000, however, for first and subsequent screens abnormal recall rates slightly exceeded the Canadian targets of less than 10% of first screens and less than 5% of rescreens.

For women in the target age range, the abnormal recall rates for first and subsequent screens are slightly higher than the national targets, which specify that less than 10% of first screens and less than 5% of rescreens should be abnormal (see Table 2). However, several Canadian programs also use CBE in combination with mammography. For women aged 50 to 69, inclusion of CBE as a screening modality has been shown to increase abnormal recall rates by as much as 58% over the rates observed if mammography were the sole detection modality¹⁴.

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