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Breast Cancer Health Center

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Breast Cancer Screening (PDQ®): Screening - Health Professional Information [NCI] - Appendix of Randomized Controlled Trials


Stockholm, Sweden 1981 [16]

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.[5]
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.[5]
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.
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