Organized Breast Cancer Screening Programs in Canada - 1996 Report

Cancers Detected Outside of Programs

Occasionally, a participant of an organized screening program is given a diagnosis of breast cancer outside of the screening program. These cancers fall into two categories: interval and non-compliant. Interval cancers are those detected in the intervals between mammographic screening. Interval cancers can be further categorized into 1) missed cancers due to technical or observer error, 2) radiographically occult cancers, i.e. those that cannot be detected by screening or diagnostic mammography but are found by other techniques, 3) "true" interval cancers, for which even retrospectively no abnormalities could be detected in the most recent screen.¹⁵ Non-compliant cancers are those detected after the program-specific recommended screening interval, when the woman does not return for a subsequent mammogram.

Provincial/territorial breast screening programs obtain information on cancers detected outside of the program through links to provincial/territorial cancer registries. Staging and pathological information is collected for these cancers, and previous mammographic films are reviewed. Radiologic and clinical audits of such cancers are important to improve the performance of breast cancer screening programs.

Complete information on cancers detected outside of screening programs is not yet available for women screened in 1996 because of the length of time needed for follow-up. For this reason, information is presented instead on women screened in 1993 (Table 12). Targets set by the U.K. Breast Screening Programme specify that not more than 12 per 10,000 women screened should present with cancer in the subsequent 24 months after screening. This target relates to women aged 50-64. Among Canadian provincial breast screening programs, 15.1 cancers per 10,000 screens among women of all ages, and 14.5 cancers per 10,000 screens among women aged 50-64 years were detected outside of programs within 24 months after screening.

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