Organized Breast Cancer Screening Programs in Canada - 1996 Report

Summary of Outcomes

Table 10 summarizes outcomes among women within the target age group (50-69 years) by province. The large variation in the proportion of first screens is a function of the length of time the program has been operating. Saskatchewan, with one of the longer running programs, had the lowest proportion of first screens (19.7%), while Newfoundland, whose program started in 1996, had the highest (99.6%). Abnormal recall rates varied among provinces: Alberta and Nova Scotia had the lowest abnormal recall rates; Manitoba, Ontario and Newfoundland, where screening visits include mammography and a clinical breast examination, had some of the highest. The higher abnormal recall rates found in Manitoba and Newfoundland may also reflect the fact that they were the two newest programs, starting in 1995 and 1996 respectively. Abnormal recall rates tend to decrease with each additional round of screening as a result of radiologists' increased experience and the availability of previous films with which to compare current examinations.

Cancer detection rates in all provinces compare favourably with the standards used by the U.K. and Australian breast screening programs (see Table 3). Positive predictive values (PPV) were highest in Alberta and Nova Scotia, where the abnormal rates were the lowest. The biopsy yield ratios reflect the overall effectiveness of the diagnostic evaluation. Diagnostic techniques such as mammography, ultrasound, fine needle aspiration or needle core biopsy should be used to the fullest before open biopsy is resorted to for diagnosis. With the exception of Newfoundland, provincial programs fall within the standards set by other countries (see Table 3), which indicate that the biopsy ratio of benign to malignant should be less than 2:1.

Table 11 summarizes outcomes by age group. Almost two-thirds of screens (65.5%) were within the target age group (50-69 years). As expected, the proportion of first screens was highest among women younger than 50 (39.1%) and lowest in women over 70 (21.4%). The rate of abnormal screens differed little by age group. The cancer detection rate increased with age, as did the positive predictive value of abnormal screening. Similarly, the benign to malignant biopsy ratio was high in women under 50, but improved with advancing age.

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