Summary of Outcomes

Table 8 summarizes outcomes for women within the target age group (50 to 69 years) by province. Quebec data capture information for the 1998 screen year only. Overall, the Canadian averages are in line with the standards of other national breast screening programs. The volume of screens and the proportion that are first screens varies greatly among provinces reflecting the length of time each program has been in operation. Abnormal recall rates drop substantially on subsequent screening as prevalent cancers are screened out in the initial screening round and previous films are available for comparison to current examinations. The abnormal recall rate is similar at third and fourth screens compared to second screens.

Figure 12 Positive predictive value of abnormal screening by age group, 1997 and 1998

Notes: Quebec data not included. Data for the New Brunswick program are incomplete and therefore do not comprehensively reflect program activity.

Cancer detection rates per 1,000 screens compare favourably with the UK and Australian program standards. Positive predictive values were highest in Alberta and Nova Scotia, where abnormal recall rates were the lowest.

Nova Scotia’s open biopsy yield ratio is particularly noteworthy. A low benign to malignant biopsy yield ratio reflects the overall effectiveness of the diagnostic evaluation in minimizing the number of women who do not have cancer but who undergo invasive procedures. Nova Scotia’s team approach to diagnosis involving the primary care physician, diagnostic radiologist, pathologist, and surgeon and frequent use of imaging-directed core biopsy has greatly decreased the need for surgery in benign lesions of the breast²².

Tumour size and lymph node status are reliable determinants of survival²³. Mammography screening aims to prevent breast cancer deaths by detecting tumours at an early stage and while they are lymph node negative. Canadian breast screening programs are on track with the standards set by other countries.

Table 9 summarizes screening outcomes by age group. Most screens were within the target age group of women aged 50 to 69. The proportion of first screens was highest among women aged 50 to 59 (47.9%) and lowest in women aged 70 and over (28.5%). The abnormal recall rate differed little among age groups. The cancer detection rate increased with age, as did the positive predictive value of abnormal screening. A high positive predictive value reflects the effectiveness of screening by determining the proportion of women who had an abnormal screen and were subsequently diagnosed with cancer. The benign to malignant biopsy ratio was high in women aged 40 to 49, but improved with age. Older women had more favourable prognostic indicators (i.e. small tumour size, node negative).

Table 10 summarizes screening outcomes for women aged 50 to 69 for the screen years 1996, 1997, and 1998. The number of screens and cancers detected increased from 1996 to 1998 as new programs began. The proportion of first screens was higher in 1998 due to the inception of Quebec’s screening program and expansion of other programs. Given an increase in the number of screening programs, the overall outcome statistics remained stable during the 3-year period and were generally within the standards set by other countries for most indicators.

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