Organized Breast Cancer Screening Programs in Canada - Report on Program Performance in 2001 and 2002

Background

With 21,600 new cases and 5,300 deaths estimated for 2005, breast cancer continues to be the most common cancer and the second leading cause of cancer death in Canadian women¹. A rise in the incidence of breast cancer has been observed over several decades; this trend parallels an increase in mammographic screening. Mortality rates continue to decline, as a result of improved treatment and early detection through mammography screening (Figures 1a and 1b).

While the body of knowledge surrounding the causes of breast cancer continues to grow, public health interventions to prevent breast cancer death in the population currently emphasize secondary prevention through mammography screening. Most known risk factors are not readily modifiable; these include demographic, genetic, hormonal

Half of all new breast cancer cases are diagnosed among women aged 50 to 69. In this group, delivery of routine, high-quality breast screening can reduce breast cancer mortality rates by as much as one-third.

and biological factors. Of these, age has the strongest influence^2,3. Both incidence and mortality rise sharply with age, with the highest rates being found among women aged 60 and over1. Half of all new cases occur among women aged 50 to 69¹.Women in this age group benefit the most from breast screening, as has been demonstrated through randomized trials. For this reason, the delivery of routine, high-quality breast screening to this group has the potential to reduce breast cancer mortality rates by as much as one-third^4,5.

Breast Cancer Screening in Canada

In December 1992, the federal government launched the first phase of the Canadian Breast Cancer Initiative (CBCI) with funding of $25 million over five years. In June 1998 the renewal of the CBCI with stable, ongoing funding of $7 million per year was announced. In September 2004 the Public Health Agency of Canada (PHAC) was created and responsibility for the CBCI became part of its mandate. Given its role in surveillance, evaluation, and best practices in public health the PHAC continues to support the activities of the National Committee for the Canadian Breast Cancer Screening Initiative, and cancer screening remains an integral component of a broader Canadian Strategy for Cancer Control.

Organized Breast Cancer Screening Programs

Organized breast cancer screening programs began in British Columbia in 1988 and have since expanded to include all provinces, the Yukon and the Northwest Territories (Table 1). To date, Nunavut has not developed an organized breast screening program. Breast cancer screening in all organized programs includes a bilateral,two-view screening mammogram. The target population is defined as asymptomatic women between the ages of 50 and 69 years with no prior diagnosis of breast cancer. All programs screen some women outside the target age group (Table 1), although they are not actively recruited to the program.

The Screening Process

Given its role in surveillance, evaluation and best practices, the Public Health Agency of Canada continues to support priorities in cancer screening through the Canadian Breast Cancer Screening Initiative and the broader Canadian Strategy for Cancer Control.

The process that an organized breast cancer screening program undertakes to reach its target population for screening can be described in three stages (Figure 2):

• Identification and invitation of the target population
• Provision of the screening examination
• If an abnormality is detected, further investigation

Women of the target age are recruited to the screening program through a letter of invitation, a physician referral or self-referral. At the screening facility, which may be a mobile unit or a fixed site, women, who do not have any breast symptoms, receive two-view mammography of each breast. In addition to mammographic screening, some programs offer clinical breast examination (CBE) performed by a trained health professional; the remaining programs encourage women to obtain regular CBE outside the program from their family physicians (Table 1). In the past, breast-self examination (BSE) was routinely taught to women. However, since the Canadian Task Force on Preventive Health Care recommended against the routine teaching of BSE to screen for breast cancer in 2001⁶, programs in British Columbia, Alberta, Saskatchewan, Manitoba, Quebec, and New Brunswick do not provide instruction in BSE, while programs in Newfoundland and Labrador, Prince Edward Island, Nova Scotia and Ontario now provide instruction in BSE only if requested by the client. Most programs continue to make educational material on BSE available to clients.

All programs provide screening results to both the woman and her physician. If the screening result is normal, women who are still eligible will be recalled by letter of invitation for another routine screen. This generally occurs after two years, although a minority of women are recalled annually on the basis of age, mammographic results, family history, or other factors that vary across programs. Women are encouraged to consult a physician if any symptoms develop in the interval before their next screening visit. Women with an abnormal screening result are informed, along with their family physician, of the need for further assessment. Depending on the program, diagnostic follow-up is coordinated either by the woman’s physician or through an integrated process coordinated by the screening program. Diagnosis is complete when a final diagnosis of either cancer or normal/benign is reached.

Canadian Breast Cancer Screening Database (CBCSD)

The CBCSD is a national breast screening surveillance system that enables organized breast cancer screening across Canada to be monitored and evaluated. Established in 1993, it is operated and maintained by the Public Health Agency of Canada’s Centre for Chronic Disease Prevention and Control, on behalf of the Canadian Breast Cancer Screening Initiative (CBCSI) and its subcommittees (Appendices 1 and 2). However, participating screening programs retain ownership of the data contained in the CBCSD.

The CBCSD currently contains screening information from program inception up to the end of 2002 for all 10 provinces (Table 2). Test data from the Northwest Territories are currently being analyzed. Because the Yukon does not have a computerized information system, its data are not available to the CBCSD. Nunavut does not have an organized program in place. Data are collected on client demographics, risk factors, screen events, referral reasons, diagnostic tests and cancers, where applicable.

The Canadian Breast Cancer Screening Database (CBCSD) is a national surveillance system operated and maintained by the Public Health Agency of Canada to conduct routine and specialized evaluation of organized screening programs and applied screening research.

Aside from its use in evaluating the performance of organized programs nationally and sub-nationally, the CBCSD is used for specialized evaluation and applied screening research. Research priorities using the CBCSD are identified on an ongoing basis. See Appendix 4 for a comprehensive list of research publications based on the CBCSD. The CBCSD is available for use by interested researchers. For up-todate information about the database, including the data dictionary and data access process, please visit this section in the on-line version of this report at: http://www.phac-aspc.gc.ca/publicat/obcsp-podcs01/ index.html.

Monitoring and Evaluation Using the Canadian Breast Cancer Screening Database

To achieve reductions in breast cancer mortality and morbidity and to minimize the unwanted effects of screening, delivery of organized screening must be of high quality. Monitoring and evaluation efforts, using the CBCSD, are used to enhance the performance of screening across Canada. A standardized method of evaluation for all Canadian organized breast cancer screening programs includes evidence-based performance measures and targets in the following categories (Table 3):

• Recruitment and retention
• Client experience
• Technical aspects
• Mammography interpretation
• Diagnostic assessment and diagnosis
• Treatment
• Survival and mortality
• Data quality assurance
• Program management

For more information regarding the development of these performance measures and targets refer to the Report from the Evaluation Indicators Working Group⁷. Due to advances in diagnostic practice, some indicators are currently under review to reflect the increased use of core biopsy to obtain a tissue diagnosis.

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