ARCHIVED - Organized Breast Cancer Screening Programs in Canada - Report on Program Performance in 2005 and 2006

Background

Introduction

An estimated 23,200 women are projected to be diagnosed with breast cancer and 5,300 women to die from the disease in 2010.⁽¹⁾ This makes breast cancer the most common form of cancer ^{[Note 2]} and the second leading cancer cause of death ^{[Note 1]} in Canadian women.⁽¹⁾ Incidence of breast cancer has risen steadily between 1980 and the early 1990's and now shows a pattern of modest decreases and increases for which the cause is unclear (Figure 1a. below ).⁽¹⁾ In addition, the mortality rate attributed to breast cancer continues to decline and is approximately 30 % lower than in 1986 (Figure 1b. pg4 ).⁽¹⁾

Early detection of breast cancer, through organized mammography screening programs, is an effective method to reduce death and morbidity associated with breast cancer. This is partially because primary prevention of breast cancer has been limited: most known risk factors are not easily modifiable.

Of known risk factors, age has the strongest influence on breast cancer incidence; roughly, half of all new cases are among women between 50 and 69 years of age. Modelling exercises have shown that the delivery of high quality breast screening programs to this age group has the potential to reduce breast cancer deaths by as much as one third.(2) Among other considerations, this scientific information influences Canadian provinces and territories to provide breast cancer screening services to this age group. Many provinces and territories also provide screening services to other age groups but in a less targeted fashion.

History of Breast Cancer Screening in Canada

In December 1992, the Canadian federal government launched the first phase of the Canadian Breast Cancer Initiative (CBCI). The CBCI included 25 million dollars over five years and included the Canadian Breast Cancer Screening Initiative (CBCSI) among its priorities. Federal funding has continued for the CBCSI, initially through Health Canada and now through the Public Health Agency of Canada.

Organized Breast Cancer Screening Programs

Canada's first organized breast cancer screening program began in British Columbia in 1988 and was followed quickly by most provinces (Table 1. pg5 ). Organized breast cancer screening programs now exist in all provinces, and the Northwest and Yukon Territories. Nunavut has not developed an organized mammography screening program but provides opportunistic screening to women when appropriate.

All organized programs provide women between 50 and 69, without a prior diagnosis of breast cancer, with a bilateral, 2-view screening mammogram biennially. Some programs also include women outside of this age group (Table 1. pg5 ) and some provide screening at more frequent intervals for a variety of reasons. In 2005 and 2006, several programs provided clinical breast examination by a nurse or technologist but most programs had phased out this service based on scientific evidence.(3) Lastly, some programs include breast cancer survivors; however, survivors are excluded from this report.

The Screening Process

Organized breast cancer screening programs offer screening to women who are asymptomatic for breast cancer. Organized programs in Canada typically involved four steps:

• Identification and invitation of the target population,
• Provision of a screening examination,
• Follow-up of any abnormalities detected at screening, and
• Recall after a normal or benign screening episode.

A number of methods are used to invite women to a screening examination and include population-based invitations, personal invitations, physician education to increase referrals, and media campaigns targeting women. Women may enter into organized programs through their personal letter of invitation, physician referral or self referral.

Screening mammograms are provided at both fixed and mobile sites. Fixed sites are located in larger urban areas while mobile sites are typically used to provide service to rural and distant communities. More recently, some mobile sites are used to supplement services at fixed sites.

Results of a screening mammogram are provided to both the woman and her physician. In general, women who have normal screening results are invited back for subsequent screening through a letter of invitation. The interval is generally 24 months; however, some women are invited back after 12 months based on their age, breast density, family history, and results of their screening. After receipt of normal results, women are encouraged to follow-up with their family physicians if they become symptomatic prior to their next scheduled screening visit.

In the case of abnormal results, both the woman and her family physician are informed. The family physician or the screening program then provides coordination of follow-up. This process varies by region. The follow-up process is resolved when a final diagnosis of cancer or normal / benign is concluded (Figure 2. pg8 ).

In addition to the systematic methods through which the individual moves through organized breast cancer screening programs, these programs also offer other advantages over opportunistic breast cancer screening. Some of these advantages include population-based recruitment, automatic recall / reminders for subsequent screening, coordinated follow-up for abnormal screening results, systematic quality assurance, and the ability to provide monitoring and evaluation of program performance.

Canadian Breast Cancer Screening Database (CBCSD)

Monitoring and evaluation of organized breast cancer screening programs through the systematic collection, analysis, and interpretation of health data, allows for the enhancement of programming across Canada. The Canadian Breast Cancer Screening Database (CBCSD) provides a method to examine and assess Canadian organized breast cancer screening programs. The CBCSD was established in 1993 and is operated and maintained by the Public Health Agency of Canada on behalf of the Canadian Breast Cancer Screening Initiative. Participating provincial and territorial screening programs contribute to the national database while retaining ownership over their data.

The CBCSD contains screening information from the inception of each organized screening program up to December 2006. At the present time Yukon does not submit records to the CBCSD. They are also excluded from the database. At every screening event, data including demographic characteristics, risk factors, the screening test, screening results and subsequent referral, diagnostic tests, outcomes, and cancer information is collected.

The database is currently used for monitoring, evaluation, and applied screening research. Research priorities are identified on an ongoing basis and the CBCSD is made available to approved researchers external to the Canadian Breast Cancer Screening Initiative. The CBCSD is committed to respecting the privacy of contributors to the dataset. All data is depersonalized and sent securely from the participating programs to the Public Health Agency of Canada. Further, the CBCSD is housed securely at the Public Health Agency of Canada: while participating in the CBCSD, the province/territory owns their data, and thus provinces/territories have unrestricted rights over their data.

Monitoring and Evaluation Using the CBCSD

Monitoring and evaluation of organized screening programs is essential to ensure Canadian women are receiving high quality services. Higher quality services result in the reduction of morbidity and mortality from breast cancer while minimizing the unwanted effects of screening. The results of monitoring and evaluation stemming from the CBCSD are used to enhance the performance of organized screening programs in Canada.

In order to provide fair evaluation for Canadian organized breast screening programs, standardized methods of evaluation have been developed. For detailed information please refer to the most recent Evaluation Indicators Working Group Report. ^{[Note 3]} The current Program Performance Measures have been adapted and updated from the previous report. In general, agreed upon performance indicators for women aged 50 to 69 include those related to recruitment and retention (participation rate, retention rate), timeliness (diagnostic interval), mammography interpretation (abnormal call rate, positive predictive value), diagnosis (invasive and in situ cancer detection rate, benign:malignant core biopsy ratio, benign open surgical biopsy rate, benign core biopsy rate), and cancer diagnosis (tumour size, node negative rate in invasive cancers, post-screen invasive cancer rate) (Table 2. pg10 ).