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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


Malmo, Sweden 1976[3,4]

Age at entry: 45 to 69 years.
Randomization: Individual, within each birth year cohort for the first phase, MMG screening trial (MMST I). Individual for the entire birth cohort 1933 to 1945 for MMST II, but with variations imposed by limited resources. Validation by analysis of age in both groups shows no significant difference.
Exclusions: In a Swedish meta-analysis, there were 393 women with pre-existing breast cancer excluded from the intervention group, and 412 from the control group. Overall however, there were 86 more women excluded from the intervention group than from the control group.
Sample size: 21,088 study and 21,195 control.
Consistency of reports: No variation in patient numbers.
Intervention: Two-view MMG every 18 to 24 months × 5.
Control: Usual care, with MMG at study end.
Compliance: Participants migrating from Malmo (2% per year) were not followed. The participation rate of study women was 74% for the first round and 70% for subsequent rounds.
Contamination: 24% of all control women had at least one MMG, as did 35% of the control women aged 45 to 49 years.
Cause of death attribution: 76% autopsy rate in early report, lower rate later. Cause of death assessment blinded for women with a breast cancer diagnosis. Linked to Swedish Cause of Death Registry.
Analysis: Evaluation, initially. Follow-up analysis, as part of the Swedish meta-analysis.[5]
External audit: No.
Follow-up duration: 12 years.
Relative risk of breast cancer death, screening versus control (95% CI): 0.81 (0.62-1.07).
Comments: Evaluation analysis required a correction factor for the delay in the performance of MMG in the control group. The two Malmo trials MMST I and MMST II have been combined for most analyses.

Ostergotland (County E of Two-County Trial), Sweden 1977[6,7,8]

Age at entry: 40 to 74 years.
Randomization: Geographic cluster, with stratification for residence (urban or rural), socioeconomic factors and size. Baseline breast cancer incidence and mortality were comparable between the randomly assigned geographic clusters. The study women were older than the control women, P < .0001, but this should not have had a major effect on the outcome of the trial.
Exclusions: Women with pre-existing breast cancer were excluded from both groups, but the numbers are reported differently in different publications. The Swedish meta-analysis excluded all women with a prior breast cancer diagnosis, regardless of group assignment.
Sample size: Variably reported, ranging from 38,405 to 39,034 in study and from 37,145 to 37,936 in control.
Consistency of reports: Variable.
Intervention: Three single-view MMGs every 2 years for women younger than 50 years and every 33 months for women 50 years and older.
Control: Usual care, with MMG at study end.
Compliance: 89% screened.
Contamination: 13% of women in the Two-County trial had MMG as part of routine care, mostly in 1983 and 1984.
Cause of death attribution: Determined by a team of local physicians. When results were recalculated in the Swedish meta-analysis, using data from the Swedish Cause of Death Registry, there was less benefit for screening than had been previously reported.
Analysis: Evaluation initially, with correction for delay in control group MMG. Follow-up analysis, as part of the Swedish meta-analysis.[5]
External audit: No. However, breast cancer cases and deaths were adjudicated by a Swedish panel that included the trial's investigators.[9]
Follow-up duration: 12 years.
Relative risk of breast cancer death, screening versus control (95% CI): 0.82 (0.64-1.05) Ostergotland.
Comments: Concerns were raised about the randomization methodology and the evaluation analysis, which required a correction for late performance of the control group MMG. The Swedish meta-analysis resolved these questions appropriately.
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