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Organized Breast Cancer Screening Programs in Canada - 1996 Report

Monitoring and Evaluation

The goal of breast cancer screening is a reduction in breast cancer deaths. A reduction of up to 40% is expected to be observed after 7 to 10 years from the point when regular attendance by 70% of women in the target age group is achieved.^3-5 Interim measures have been identified that can help determine whether a program is on course in leading to a reduction in breast cancer deaths.

On the basis of the results from a Swedish randomized trial of breast screening, Day, Williams and Khaw⁸ identified three measures that are important to monitor: compliance measures, screening characteristics such as cancer detection rate at first screen, and rate of advanced cancers. Achieving a favourable outcome in each of these interim measures is necessary before breast cancer screening programs can achieve reductions in breast cancer mortality. Other interim measures identified as helpful in monitoring programs are the evaluation of test performance and a description of diagnostic work-up. Similarly, Tabar et al⁹ developed specific targets for screening programs based on a Swedish randomized trial of mammographic screening for breast cancer. These targets are presented in Table 3 along with the standards set by the Europe Against Cancer Programme,¹⁰ the United Kingdom NHS Breast Screening Programme,¹¹ and the Australian National Program for the Early Detection of Breast Cancer.¹² While national standards or indicators have not been adopted in Canada, provincial/territorial screening programs aim to achieve the standards set by other organized programs and monitor their performance accordingly.

Table 3 Standards for Breast Screening Programs
Indicator	Tabar et al, 1992⁹	Europe¹⁰	United Kingdom¹¹	Australia¹²
Attendance rate		>= 60% (ages 50-64)	>= 70% (ages 50-64)	70% (ages 50-69)
Abnormal recall rate (%) Initial screen Rescreen	<= 9 (overall)	< 7 < 5	< 10 < 7	< 10 < 5
Cancer detection rate Initial screen Rescreen	>= 3xIR* (overall)	>= 3xIR* 1.5xIR*	>= 2.7 per 1,000* >= 3.0 per 1,000*	> 50 in 10,000 > 20 in 10,000
Benign to malignant biopsy ratio Initial screen Rescreen	< 3:1 (overall)	< 2:1 < 1:1		<= 2:1 <= 1:1
Invasive cancers < 15 mm	> 50%	25% (<= 10 mm)	>= 1.5 per 1,000 (initial) >= 1.65 per 1,000 (rescreen)	> 8 per 10,000 (<= 10 mm)
Rate of cancer without lymph node invasion (%)	>= 70%
Detected cancers that are in situ Initial screen Rescreen			0.4 - 0.9 per 1,000* 0.5 - 1.0 per 1,000*	10-20%
Rate of cancers presenting between screening episodes			1.2 per 1,000 screened women within 2 years of screen	< 6 per 10,000 screened women within 1 year of screen
* IR = expected incidence rate in the absence of screening Invasive cancers only, excludes cancers that are purely in situ (noninvasive or intraductal) * Based on women between the ages of 50 to 52.9 attending for initial screen and women between the ages of 53 and 64.9 attending for rescreens

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