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Tables
- Table 1:
Breast cancer mortality using mammography with or without clinical breast examination*15
Age, yr Range of follow-up, yr No. and design of studies Women who die from breast cancer, %† Women who are not screened: risk of dying of breast cancer per 100015 Relative risk (95% CI)‡ Women who are screened: risk of dying from breast cancer per 1000 (95% CI) Absolute effect per 1000 (95% CI) Number needed to screen (95% CI) GRADE rating of certainty of evidence Mammogram with or without clinical breast examination Usual care, % 40–49 17.7 to 25.7 8 RCTs23, 33–37¶ Unavailable†† 0.4 3.85 0.85 (0.78 to 0.93) 3.27 (3.00 to 3.58) 0.58 fewer (0.27 fewer to 0.85 fewer) 1724 (1176 to 3704) ⊕⊕○○
LOW‡‡50–59§ 18 to 30 6 RCTs33, 35–37¶ Unavailable†† 0.5 5.00 0.85 (0.78 to 0.93) 4.25 (3.90 to 4.65) 0.75 fewer (from 0.35 fewer to 1.10 fewer) 1333 (909 to 2857) ⊕○○○
VERY LOW§§60–69 13.1 to 30 4 RCTs23,33,35–36** Unavailable†† 0.6 6.15 0.85 (0.78 to 0.93) 5.23 (4.80 to 5.72) 0.92 fewer (from 0.43 fewer to 1.35 fewer) 1087 (741 to 2326) ⊕⊕○○
LOW‡‡70–74 13.2 to 13.6 2 RCTs23,35 Unavailable†† 1.0 10.31 0.85 (0.78 to 0.93) 8.76 (8.04 to 9.59) 1.55 fewer (from 0.72 fewer to 2.27 fewer) 645 (441 to 1389) ⊕○○○
VERY LOW ¶¶Note: CI = confidence interval, GRADE = Grading of Recommendations Assessment, Development and Evaluation system, RR = relative risk.
↵* This table presents screening outcomes based on short-case accrual methods. The systematic review conducted for this guideline presents screening outcomes using both short- and long-case accrual methods.15 In short-case accrual (initial + 7 subsequent screens; 23 years of follow-up), only those cases diagnosed during the screening period are included (median 7 yr; range 3 to 12 yr), whereas long-case accrual (initial + 4 subsequent screens; 14 years of follow-up) includes all cases diagnosed to the end of the follow-up period. Short-case accrual reduces bias from contamination because women in the control group would not have been screened until the trial was over, while long-case accrual may underestimate the benefits of screening as women in the control group are more likely being screened after the trial.15
↵† The baseline risk in the control groups may not have been representative of all included studies because the numerators or denominators were either unclear or not reported.
↵‡ A subgroup analysis of relative risk by age was assessed based on published methodology.31,32 No difference in RR among subgroups was detected and true differences resulting from age were deemed unlikely. The use of the all-ages RR data rather than focusing on each decade of age aligns with this assessment. It is appropriate to use control event rates relevant to each age group to determine corresponding risks, with attendant implications on absolute benefit (calculations provided in Appendix 4).
↵§ Presents results with control group at moderate baseline risk.
↵¶ The Stockholm and Gothenburg trials were considered quasi-randomized.33
↵** The Stockholm trial was considered quasi-randomized.23
↵†† Complete data were not available. Numerators or denominators were either unclear or not reported for all included studies.
↵‡‡ Very serious concerns about risk of bias because randomization and allocation concealment were either not reported or had serious deficiencies.
↵§§ Very serious concerns about risk of bias because randomization and allocation concealment were either not reported or had serious deficiencies and there were serious concerns about inconsistency, as heterogeneity may be moderate (I2 = 26%; p value = 0.24) and there were serious concerns about imprecision because, although the number of events and total population are large (> 300 threshold for events), the 95% CIs include the null and do cross appreciable benefit (RR 0.75).
↵¶¶ Very serious concerns about risk of bias because randomization and allocation concealment were either not reported or had serious deficiencies and there were serious concerns about imprecision because, although the total population is large (> 2000), the 95% CIs include the null and do cross appreciable benefit (RR 0.75).
Age of women at initial screen, yr Years after screening Breast cancers estimated as overdiagnosed, % Invasive and in situ cancers, % Invasive cancers, % 40 to 49 5 41 32 20 55 48 50 to 59 5 25 16 20 16 5 ↵* Overdiagnosis by age was estimated using this calculation: The numerator is the difference in numbers of cancers in the mammography arm less those in the control arm; and the denominator is the number of screen-detected cancers in the mammography arm.39 Only the findings from the estimate on overdiagnosis from a Canadian randomized controlled trial39 are included because it provided an estimate by age and was appraised as being at moderate risk of bias.15
- Table 3:
False-positives and unnecessary biopsies from an estimated cohort of women in a breast screening program for 7 years of screening*47
Age range, yr Outcome 40–49 50–59 60–69 70–74 Per 1000 women screened† FP mammography 294 294 256 219 Biopsies on FP 43 37 35 30 Per 1 breast cancer death prevented FP mammography (based on 3 cycles of screening)† 508 392 (M) 278 141 Biopsies on FP (based on 3 cycles of screening)† 74 50 (M) 38 19 Note: FP = false-positive, M = calculated using the moderate baseline risk for this age group.15
↵* As the median duration of screening trials was 7 years (range 3–12 yr), the impact of this duration of screening on benefits and harms was used. The data are used to approximate a cohort of women entering the screening program.47 Although assumed, but not confirmed, the “initial screen” in the Canadian Partnership Against Cancer report is the first screen documented in the database and may not necessarily be the first “true” screen of a woman. This is especially true for data originating from Alberta.
↵† Three cycles of screening for which women are screened every 2–3 years, for a total of 6–9 years of a screening period. Calculation: Initial screening cycle + 2 (subsequent screening cycle) to estimate harms occurring with 7 years of screening.
Organization Recommendations Canadian Task Force on Preventive Health Care (current guideline, 2018) Recommendations apply to breast cancer screening for women aged 40 to 74 years who are not at increased risk of breast cancer:
Mammography:For women aged 40 to 49 years, we recommend not screening with mammography; the decision to undergo screening is conditional on the relative value a woman places on possible benefits and harms from screening (conditional recommendation; low-certainty evidence).
For women aged 50 to 69 years, we recommend screening with mammography every 2 to 3 years; the decision to undergo screening is conditional on the relative value that a woman places on possible benefits and harms from screening (conditional recommendation; very low-certainty evidence).
For women aged 70 to 74 years, we recommend screening with mammography every 2 to 3 years; the decision to undergo screening is conditional on the relative value that a woman places on possible benefits and harms from screening (conditional recommendation; very low-certainty evidence).
Recommendations on using screening modalities other than mammography for breast cancer screening:We recommend not using MRI, tomosynthesis or ultrasound to screen for breast cancer in women who are not at increased risk (strong recommendation; no evidence).
We recommend not performing clinical breast examinations to screen for breast cancer (conditional recommendation; no evidence).
We recommend not advising women to practise breast self-examination to screen for breast cancer (conditional recommendation; low-certainty evidence).
Canadian Task Force on Preventive Health Care (2011)5 Recommendations apply to women aged 40 to 74 years at average risk of breast cancer:
Mammography:For women aged 40–49 years, we recommend not routinely screening with mammography (weak recommendation; moderate-quality evidence).
For women aged 50–69 years, we recommend routinely screening with mammography every 2 to 3 years (weak recommendation; moderate-quality evidence).
For women aged 70–74 years, we recommend routinely screening with mammography every 2 to 3 years (weak recommendation; low-quality evidence).
We recommend not routinely screening with MRI scans (weak recommendation; no evidence).
We recommend not routinely performing clinical breast examinations alone or in conjunction with mammography to screen for breast cancer (weak recommendation; low-quality evidence).
We recommend not advising women to routinely practise breast self-examination (weak recommendation; moderate-quality evidence).
United States Preventive Services Task Force (2016)88 Biennial screening mammography for women aged 50 to 74 years (Grade B recommendation).
The decision to start screening mammography in women before age 50 years should be an individual one. Women who place a higher value on the potential benefit than the potential harms may choose to begin biennial screening between 40 and 49 years of age (Grade C recommendation).
For women aged 75 years or older, current evidence is insufficient to assess the balance of benefits and harms of screening mammography (I statement).
For all women, current evidence is insufficient to assess the benefits and harms of digital breast tomosynthesis as a primary screening method for breast cancer (I statement).
For women with dense breasts, current evidence is insufficient to assess the balance of benefits and harms of adjunctive screening for breast cancer following a negative mammogram using breast ultrasonography, MRI, digital breast tomosynthesis, or other methods in women identified to have dense breasts on an otherwise negative screening mammogram (I statement).American Cancer Society (2015)89 Women with an average risk of breast cancer should undergo regular screening mammography starting at age 45 years (strong recommendation).
Women aged 45 to 54 years should be screened annually, transitioning to biennial screening at 55 years of age with the option to continue annual screening (qualified recommendations).
Women between the ages of 40 and 44 years should have the opportunity to begin annual screening (qualified recommendation).
Healthy women should continue screening mammography as long as they have a life expectancy of 10 years or longer (qualified recommendation).
The American Cancer Society does not recommend clinical breast examination for breast cancer screening among average-risk women at any age (qualified recommendation).UK National Health Service Breast Screening Programme (2015)90 The UK National Screening Committee recommends that all eligible women aged 50 to 70 years be invited to breast cancer screening every 3 years.
Eligible women, aged 50 to 70, receive an invitation letter explaining the program, as well as benefits and risks of breast screening:Women do not always receive an invitation when they turn 50. They can expect their invitation within 3 years of their 50th birthday.
Women cannot walk in and request breast screening unless they are older than 70, when they can request screening every 3 years.
Cancer Australia (2015)91 It is recommended that women of all ages, and regardless of whether they attend mammographic screening, are aware of how their breasts normally look and feel and report any new or unusual changes promptly to their general practitioner.
No one method for women to use when checking their breasts is recommended over another.
It is recommended, to reduce the risk of death from breast cancer, that women aged 50–74 years attend the BreastScreen Australia Program for free 2-yearly screening mammograms, having considered the benefits and downsides.
Mammographic screening is not recommended for women younger than 40 years of age.
Women aged 40–49 years and 75 years and older are eligible to receive free screening mammograms through the BreastScreen Australia Program, but they do not receive an invitation to attend. In deciding whether to attend for screening mammography, women in these age groups should balance the potential benefits and downsides for them. For women of all ages who are at increased risk of developing breast cancer, it is recommended that an individualized surveillance program be developed in consultation with the woman’s general practitioner or specialist.Note: MRI = magnetic resonance imaging.
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