EXECUTIVE SUMMARY

Breast cancer continues to be the most common cancer afflicting Canadian women and nearly half of all new cases occur among those aged 50 to 69. For women in this age group, randomized trials and demonstration projects initiated in the 1970s and 1980s indicated that breast screening delivered in an organized and systematic manner was an effective means of reducing the rate of death from breast cancer by approximately one third. In December 1992, under the Canadian Breast Cancer Screening component of the Canadian Breast Cancer Initiative, Health Canada was mandated to facilitate a federal/provincial/territorial working group on breast cancer screening to implement and evaluate breast cancer screening programs in Canada. In response, provincial/territorial breast cancer screening programs collaborated in the development of a national database to monitor and evaluate breast cancer screening delivered through organized provincial programs. This document, the second in a series of biennial reports, is a product of the continuous evaluation that organized breast cancer screening programs undergo to assure high standards are maintained in the provision of an effective service. It presents selected statistics for the 1997 and 1998 calendar years using data submitted by provincial screening programs to the Canadian Breast Cancer Screening Database.

Over the past decade, breast screening through provincially organized breast cancer screening programs has grown substantially, from a single program offering two-view mammographic screening to 9,371 eligible women in 1989, to nine organized programs screening a total of 470,876 women in 1998. The dramatic rise in the number of women screened through organized programs, and the establishment of new programs in several jurisdictions, heightens the importance of quality screening. This report demonstrates that women attending organized breast screening programs in Canada continue to receive screening that meets or exceeds most standards set by other countries. In 1997 and 1998, abnormal recall rates (mammography alone) on first and rescreen for women aged 50 to 69 were within the United Kingdom's recommendations. The benign to malignant open biopsy ratio of 1.6:1.0 and cancer detection rate on first and rescreen of 6.7 and 4.2 per 1,000 screens respectively, were within targets set by other countries. Overall, 37.6% of detected invasive cancers were <= 10mm and 78.5% of cancers were lymph node negative, exceeding the recommendations of other national breast screening programs. Participation rates within organized Canadian programs remain sub-optimal, reaching between 11.5% and 54.7% of the target population. In order to reach a 70% participation rate, additional resources are necessary for the implementation of new programs and the expansion of existing ones. In addition, a significant number of women continue to receive opportunistic screening in the diagnostic sector across Canada. With the growth of organized screening, steady improvement towards achieving a cancer control target of 70% participation among women aged 50 to 69 is expected.

Provincial breast cancer screening programs have grown from a single program screening 9,371 eligible women in 1989, to nine programs screening 470,876 women in 1998.

Although increasing recruitment to attain at least a 70% participation rate in organized screening among women aged 50 to 69 remains an important goal of organized programs, attention is also focused on ensuring that previously screened asymptomatic women continue to receive the benefits of regular breast screening. With respect to retention, organized breast cancer screening programs have fared remarkably well. Among women screened in 1994 and 1995 who were eligible for a repeat biennial mammogram, approximately 80% returned to their programs within 2.5 years of their previous screen. Compared with women who delayed their return to screening beyond 2.5 years, those who returned within 2.5 years had fewer abnormalities or cancers that were detected compared to women who returned in a less timely interval, while high positive predictive values of the screening examination were maintained.

In the coming years, organized screening programs will continue their efforts towards providing quality breast cancer screening. Programs are continually updating their efforts to achieve a population-based breast cancer mortality reduction by reviewing new evidence and contributing to the growing body of research on screening. The Canadian Breast Cancer Screening Database is contributing to this effort by supporting research activities that influence policy development in breast cancer screening.

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