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Effect of Screening on Breast Cancer Mortality


Stockholm, Sweden 1981 [18]

Age at entry: 40 to 64 years.
Randomization: Cluster by birth date. There were two subtrials with balanced randomization in the first and a significant imbalance in the second with 508 more women in the screened group than the control.
Exclusions: Inconsistently reported.
Sample size: Declined from 40,318 to 38,525 in intervention group and rose from 19,943 to 20,978 in control, between published reports.
Consistency of reports: Variable.
Intervention: Single-view MMG every 28 months × 2.
Control: MMG at year 5.
Compliance: 82% screened.
Contamination: 25% of women entering the study had MMG in the 3 years before entry.
Cause of death attribution: Linked to Swedish Cause of Death Registry.
Analysis: Evaluation, with 1-year delay in the posttrial MMG in control group. Follow-up analysis as part of the Swedish meta-analysis.[3]
External audit: No.
Follow-up duration: 8 years.
Relative risk of breast cancer death, screening versus control (95% CI): 0.80 (0.53-1.22).
Comments: There are concerns about randomization, especially in the second subtrial, about exclusions, and about the delay in control group MMG. Inclusion of these data in the Swedish meta-analysis resolves many of these questions.

Gothenberg, Sweden 1982

Age at entry: 39 to 59 years.
Randomization: Complex; cluster randomly assigned within birth year by day of birth for older group (aged 50-59 years) and by individual for younger group (aged 39-49 years); ratio of study to control varied by year depending on MMG availability (randomization took place 1982-1984).
Exclusions: A similar proportion of women were excluded from both groups for prior breast cancer diagnosis (1.2% each).
Sample size: Most recent publication: 21,650 invited; 29,961 control.
Consistency of reports: Variable.
Intervention: Initial two-view MMG, then single-view MMG every 18 months × 4. Single-read first three rounds, then double-read.
Control: Control group received one screening exam approximately 3 to 8 months after the final screen in study group.
Cause of death attribution: Linked to Swedish Cause of Death Registry; also used an independent endpoint committee.
Analysis: Both evaluation and follow-up methods.[3]
External audit: No.
Follow-up duration: 12 to14 years.
Relative risk of breast cancer death, screening versus control (95% CI): Aged 39 to 59 years: 0.79 (0.58-1.08) [evaluation]; 0.77 (0.60-1.00) [follow-up].
Comments: No reduction for women aged 50 to 54 years, but similar reductions for other 5-year age groups.
Conclusions: Delay in the performance of MMG in the control group and unequal numbers of women in invited and control groups (complex randomization process) complicates interpretation.

AGE Trial[19]

Age at entry: 39 to 41 years.
Randomization: Individuals from lists of general practitioners in geographically defined areas of England, Wales, and Scotland; allocation was concealed.
Exclusions: Small (n = 30 in invited group and n = 51 in not invited group) number excluded in each group because could not locate or deceased.
Sample size: 160,921 (53,884 invited; 106,956 not invited).
Consistency of reports: Not applicable.
Intervention: Invited group aged 48 years and younger offered annual screening by MMG (double-view first screen, then single mediolateral oblique view thereafter); 68% accepted screening on first screen and 69% to 70% were reinvited (81% attended at least one screen).
Control: Those who were not invited received usual medical care, unaware of their participation, and few screened prior to randomization.
Cause of death attribution: From the National Health Service (NHS) central register, death certificate code accepted.
Analysis: Follow-up method intention-to-treat (though all women aged 50 years would be offered screening by NHS).
External audit: None.
Follow-up duration: 10.7 years.
Relative risk of breast cancer death, screening versus control (95% CI): 0.83 (0.66-1.04).
Conclusions: Not a statistically significant result, but fits with other studies.

WebMD Public Information from the National Cancer Institute

Last Updated: October 07, 2011
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