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- Duffy, S.W., et al.
(författare)
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The Swedish two-county trial of mammographic screening : Cluster randomisation and end point evaluation
- 2003
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Ingår i: Annals of Oncology. - : Elsevier BV. - 0923-7534 .- 1569-8041. ; 14:8, s. 1196-1198
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Tidskriftsartikel (refereegranskat)abstract
- Background: The Swedish Two-County Trial has been criticised on the grounds of the cluster randomisation and alleged bias in classification of cause of death. Patients and methods: In the Two-County Trial, 77080 women were randomised to regular invitation to screening (active study population, ASP) and 55985 to no invitation (passive study population, PSP), in 45 geographical clusters. After ~7 years, the PSP was invited to screening and the trial closed. We analysed data using hierarchical statistical models to take account of cluster randomisation, and performed a conservative analysis assuming a systematic difference between ASP and PSP in baseline breast cancer mortality in one of the counties. We also analysed deaths from causes other than breast cancer and from all causes among breast cancer cases diagnosed in the ASP and PSP. Results: Taking account of the cluster randomisation there was a significant 30% reduction in breast cancer mortality in the ASP. Conservatively, assuming a systematic difference between ASP and PSP clusters in baseline breast cancer mortality, there was a significant 27% reduction in mortality in the ASP. Ignoring classification of cause of death, there was a significant 13% reduction in all-cause mortality in breast cancer cases in the ASP. Conclusions: Breast cancer mortality is a valid end point and mammographic screening does indeed reduce mortality from breast cancer. The criticisms of the Swedish Two-County Trial are unfounded.
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| 2. |
- Tabar, L., et al.
(författare)
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All-cause mortality among breast cancer patients in a screening trial : Support for breast cancer mortality as an end point
- 2002
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Ingår i: Journal of Medical Screening. - : SAGE Publications. - 0969-1413 .- 1475-5793. ; 9:4, s. 159-162
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Tidskriftsartikel (refereegranskat)abstract
- Background: It has recently been suggested that all-cause mortality is a more appropriate end point than disease specific mortality in cancer screening trials, and that disease specific mortality is biased in favour of screening. This suggestion is based partly on supposed inconsistencies between all-cause mortality results and disease specific results in cancer screening trials, and alleged increases in deaths from causes other than breast cancer among breast cancer cases diagnosed among women invited to screening. Methods: We used data from the Swedish Two-County Trial of mammographic screening for breast cancer, in which 77 080 women were randomised to an invitation to screening and 55 985 to no invitation. We estimated relative risks (RRs) (invited v control) of death from breast cancer, death from other causes within the breast cancer cases, and death from all causes within the breast cancer cases. RRs were adjusted for age and took account of the longer follow up of breast cancer cases in the invited group due to lead time. Results: There was a significant 31% reduction in breast cancer mortality in the invited group (RR 0.69, 95% confidence interval (Cl) 0.58-0.80, p
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| 3. |
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| 4. |
- Warwick, J., et al.
(författare)
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Time-Dependent Effects on Survival in Breast Carcinoma : Results of 20 Years of Follow-Up from the Swedish Two-County Study
- 2004
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Ingår i: Cancer. - : Wiley. - 0008-543X .- 1097-0142. ; 100:7, s. 1331-1336
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND. Tumor size, lymph node status, and histologic grade are reported to be important predictors of survival in the first 5 years after the diagnosis of invasive breast carcinoma. However, to the authors' knowledge, the effect of these factors in the longer term (> 10 years after diagnosis) is not yet clear. METHODS. It is now > 20 years since the Swedish Two-County Trial of breast carcinoma screening with mammography was instigated and long-term follow-up is now available to December 1998. In the current study, the authors analyzed the effects of tumor size, lymph node status, and tumor grade on survival to death from breast carcinoma using Cox regression and frailty models that allow the baseline hazard and/or effect of a covariate to vary with time. RESULTS. The effects of tumor size, lymph node status, and tumor grade were shown to progressively diminish with time from diagnosis. The Cox regression model with time-varying coefficients and a dampening parameter then was fitted to allow for the attenuation of prognostic effects, tumor size, lymph node status, and tumor grade were all found to be highly significant (P < 0.001). CONCLUSIONS. The results of the current study suggest that long-term survival in women with invasive breast carcinoma could be modelled satisfactorily using either frailty models or Cox regression models with time-varying coefficients. The results also suggest that the value of tumor grade, lymph node status, and tumor size at the time of diagnosis have a lasting influence on subsequent survival, albeit attenuated in later years. The long-term effects of these prognostic factors may explain the fact that the impact of mass screening programs on breast carcinoma mortality rates is still apparent many years later. © 2004 American Cancer Society.
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