Organized Breast Cancer Screening Programs in Canada

1999 and 2000 Report

Summary of Performance Measures

Organized screening programs are committed to maximizing the benefits of screening by detecting as many cancers as possible as early as possible, and by minimizing potential harms by eliminating as much as possible diagnostic follow-up among women who do not have cancer. To transfer these benefits to the entire target population, screening programs must attempt to reach as many eligible women as possible by maximizing ongoing participation. 

Only 30.2% of eligible women accessed organized screening nationally. Greater participation in organized programs by the target population will bring the benefits of screening to more Canadian women.

The extent to which programs maximize benefits to participants is reflected by indicators for the rate of invasive cancer detection, the proportion of small invasive cancers and the proportion of invasive cancers that have not spread to the lymph nodes. Invasive cancer detection rates for mammography and combined screening (mammo-
graphy and/or CBE) exceeded Canadian performance targets for rescreened women, but just fell short for women on initial screen. The proportions of small and of node negative invasive cancer were well within targets (Table 8). Post-screen cancer detection rates reflect the sensitivity of screening. Within 12 months of the screening examination, this rate bordered on the Canadian target; within 24 months it was well within target. Although not all cancers are detectable by screening, this measure monitors whether the number of cancers missed is being kept to a minimum. 

Indicators for abnormal recall rate, positive predictive value, benign to malignant open biopsy ratio and the timeliness of the diagnostic interval measure the degree to which programs minimize the potential harms of screening among participants. Abnormal recall rates for mammography and for any modality exceeded the national targets
of < 10% and < 5%. PPVs were within target, as were benign to malignant open biopsy ratios. Nationally, 73.3% of women not requiring surgical biopsy were given a diagnosis within five weeks
and 45.6% of women requiring surgical biopsy received a diagnosis within seven weeks. No individual program met the 90% target for timely diagnostic interval. 

Transferring the benefits of screening to the entire target population remains a challenge for screening programs. Although most programs saw increased participation in 1999 and 2000, only 30.2% of eligible women accessed organized screening nationally. Greater participation in organized programs by the target population will bring the benefits of screening to more Canadian women. The performance indicator for retention indicates that programs are successfully maintaining the participation of women who enter the screening program. 

Table 8 further details the outcomes for women within the target population by province. The provincial results are presented for summary purposes only, as it is difficult to readily compare the performance of all programs. The volume of screens and the proportion that are first screens vary greatly among provinces, mainly reflecting the length of time each program has been in operation. Programs also differ in terms of screening methods; Manitoba, Ontario, Nova Scotia, Prince Edward Island and Newfoundland each offer CBE in addition to mammography. This has an impact on both abnormal recall rates and cancer detection. Variations among the provinces in risk factor profiles, socio-economic status and the age distribution of women may also have an impact on the performance of the screening programs. 

While the performance of individual programs is not comparable,
the results in Table 8 do illustrate some of the successes of program- specific approaches. For the most part, cancer detection rates compare favourably with the Canadian performance targets (Table 2). PPVs were highest in Alberta and Nova Scotia, where abnormal recall rates were the lowest. Benign to malignant biopsy ratios have improved in most programs and this, in turn, has improved the combined national ratios. Increased use of imaging-directed core biopsy has greatly decreased the need for surgery in the case of benign lesions and can lead to a more timely definitive diagnosis. Although no program currently meets the performance targets for timely diagnosis, Nova Scotia came closest to meeting the target. More frequent use of core biopsy to obtain a tissue diagnosis and the use of patient navigators are two reasons for the increased timeliness of diagnosis in this program. The recent adoption of facilitated referral practices, in which the screening program arranges the initial diagnostic imaging procedures on behalf of a woman's family physician, has led to substantial improvements in timeliness in a number of programs^19,20. 

Table 9 summarizes screening outcomes by age group. Most screens occurred within the target age group. As expected, the proportion of first screens was highest among women aged 50 to 59 (53.7%) and lowest in women aged 70 and over (20.2%). The abnormal recall rate differed little among age groups. The cancer detection rate increased with age, as did the PPV of abnormal screening. The benign to malignant biopsy ratios were higher in women aged 40 to 49 but improved with age. Older women tended to have more favourable prognostic indicators (i.e. small tumour size, node negative). 

Table 10 summarizes screening outcomes for women aged 50 to 69 for the past five screen years (1996, 1997, 1998, 1999 and 2000). The number of screens and cancers detected increased from 1996 to 1999 as new programs began to operate at capacity. However, from 1999 to 2000 there was very little growth, suggesting that many programs have reached their capacity to recruit additional women. Consequently, program-based screening mammography is potentially available to only 1.3 million of the estimated 3 million Canadian women aged 50 to 69. Abnormal recall rates increased over time for both first and subsequent screens, leaving performance targets unmet, while cancer detection rates remained stable. This emphasizes that further efforts are required to ensure that the number of healthy women who experience follow-up procedures is minimized. 

Table 9
Screening outcome summary by age group, 1999 and 2000 screen years

Outcome	40-49	50-59	60-69	70+	All Ages
Number of screens	208,881	581,760	387,012	132,623	1,310,276
Number of first screens	79,256	312,751	164,129	26,838	582,974
Number of cancersab	417	2,646	2,442	1,076	6,581
Participation rate (%)	6.3	30.4	29.3	7.6	16.7
Retention rate (%)c	67.8	76.2	78.6	70.1	74.6
Abnormal recall rate (%)
Abnormal by mammographyd     Initial  screen     Rescreen	11.9 5.5	11.7 6.0	10.4 5.7	9.9 5.1	11.3 5.7
Abnormal by any mode of dectection     Initial  screen     Rescreen	12.0 5.5	12.5 7.0	11.1 6.9	11.2 6.2	12.0 6.6
Invasive cancer detection rate per 1,000 screensa
Detected by mammographyd     Initial  screen     Rescreen	1.9 1.1	4.1 2.7	6.3 4.2	11.0 5.4	4.7 3.3
Detected by any mode of dectection     Initial  screen     Rescreen	1.9 1.1	4.1 2.8	6.3 4.3	11.1 5.5	4.7 3.4
In situ cancer detection rate per 1,000 screensa
Initial  screen     Rescreen	0.8 0.5	1.1 0.9	1.3 1.0	1.6 1.3	1.1 0.9
Completed diagnostic interval (%)e
With no open biopsy, within 5 weeks     With open biopsy, within 7 weeks	75.0 40.3	72.9 44.4	74.0 47.3	74.9 49.1	73.7 45.8
Positive predictive value (%)ab
Detected by mammographyd     Initial  screen     Rescreen	2.2 3.0	4.6 6.1	7.4 9.4	12.8 13.3	5.3 7.5
Detected by any mode of dectection     Initial  screen     Rescreen	2.2 2.9	4.3 5.3	7.0 7.9	11.3 11.3	5.0 6.6
Benign to malignant open biopsy ratioe	3.1 : 1	1.7 : 1	1.0 : 1	0.6 : 1	1.3 : 1
Benign to malignant core biopsy ratioe	5.3 : 1	2.4 : 1	1.4 : 1	0.9 : 1	1.9 : 1
Invasive cancer tumour size (% £ 10 mm)ef	31.9	36.1	39.9	38.6	37.7
Positive lymph nodes in cases of invasive cancer (%)ef	26.5	27.5	21.2	16.7	22.9
Post-screen detected invasive cancer rate (per 10,000 person-years)g
Within 12 months     Within 24 months	4.7 6.3	5.8 9.3	6.3 10.1	6.1 9.5	5.8 9.1

^a    Only first screens, with one year of follow-up, are included for Quebec data. 

^b    Includes invasive, in situ, and unclassified cancers. 

^c    Retention rates are calculated on 1996 and 1997 data and include the following provinces: British Columbia, Alberta, Saskatchewan, Manitoba,
    Ontario, New Brunswick, Nova Scotia, and Newfoundland. 

^d    Independent of CBE delivery or CBE findings. 

^e    Quebec data are not reported for this indicator. 

^f    Missing values were exluded from calculations; expressed as a proportion of invasive cancers with complete data on tumour size or number of
    positive nodes. 

^g    Post-screen detected cancer rates are calculated on 1996 and 1997 data and include the following provinces: British Columbia, Alberta,
    Manitoba, Ontario, and Newfoundland. 

Table 10
Screening outcome summary by year, women aged 50-69 at screening 

	Year of Screen
Outcome	1996	1997	1998	1999	2000
Number of screens	215,415	246,429	328,126	466,682	502,090
Number of first screens	83,627	92,316	154,936	247,941	228,939
Number of cancersab	1,059	1,319	1,437	2,568	2,520
Retention rate (%)c	78.3	80.3	86.3	N/A	N/A
Abnormal recall rate (%)
Abnormal by mammographyd     Initial  screen     Rescreen	8.8 4.6	9.1 5.0	10.2 5.4	11.2 5.8	11.4 5.8
Abnormal by any mode of dectection     Initial  screen     Rescreen	10.7 5.6	10.8 6.0	11.3 6.5	11.9 7.0	12.1 6.9
Invasive cancer detection rate per 1,000 screensa
Detected by mammographyd     Initial  screen     Rescreen	4.9 3.4	5.5 3.5	5.0 3.2	4.9 3.5	4.7 3.3
Detected by any mode of dectection     Initial  screen     Rescreen	5.0 3.4	5.6 3.7	5.1 3.3	5.0 3.6	4.7 3.4
In situ cancer detection rate per 1,000 screensa
Initial  screen     Rescreen	1.1 0.7	1.2 0.8	1.4 0.8	1.2 0.9	1.1 0.9
Completed diagnostic interval (%)e
With no open biopsy, within 5 weeks     With open biopsy, within 7 weeks	75.9 56.0	75.9 52.8	74.9 51.2	73.0 45.2	73.5 46.1
Positive predictive value (%)ab
Detected by mammographyd     Initial  screen     Rescreen	6.8 8.9	7.4 8.7	6.2 7.4	5.6 7.7	5.3 7.5
Detected by any mode of dectection     Initial  screen     Rescreen	5.7 7.4	6.3 7.5	5.5 6.3	5.3 6.5	5.0 6.4
Benign to malignant open biopsy ratioe	1.5 : 1	1.5 : 1	1.6 : 1	1.4 : 1	1.2 : 1
Benign to malignant core biopsy ratioe	1.9 : 1	1.9 : 1	2.1 : 1	2.0 : 1	1.8 : 1
Invasive cancer tumour size (% £ 10 mm)ef	37.3	37.5	38.6	38.6	37.4
Positive lymph nodes in cases of invasive cancer (%)ef	22.7	22.6	20.6	24.6	24.1
Post-screen detected invasive cancer rate (per 10,000 person-years)g
Within 12 months     Within 24 months	6.4 9.4	5.6 9.9	N/A N/A	N/A N/A	N/A N/A

^a    Only first screens, with one year of follow-up, are included for Quebec data. 

^b    Includes invasive, in situ, and unclassified cancers. 

^c    Retention rate calculations include the following provinces: British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, New Brunswick,
    Nova Scotia, and Newfoundland. 

^d    Independent of CBE delivery or CBE findings. 

^e    Quebec data are not reported for this indicator. 

^f    Missing values were exluded from calculations; expressed as a proportion of invasive cancers with complete data on tumour size or number of
    positive nodes. 

^g    Post-screen detected cancer rates are calculated on 1996 and 1997 data and include the following provinces: British Columbia, Alberta,
    Manitoba, Ontario, and Newfoundland. 

 

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