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- Duffy, SW, et al.
(författare)
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Correcting for non-compliance bias in case-control studies to evaluate cancer screening programmes
- 2002
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Ingår i: The Journal of the Royal Statistical Society, Series C. - 0035-9254 .- 1467-9876. ; 51, s. 235-243
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Tidskriftsartikel (refereegranskat)abstract
- In the evaluation of uncontrolled service screening programmes for cancer, the case-control design is sometimes used, in which people who die from the disease in question are compared with live controls with respect to screening histories, Such a design tends to yield estimates of relative mortality in voluntary participants compared with non-participants. This may bias results, since compliers and non-compliers may differ a priori in ways which are not related to screening but which nevertheless affect the risk of death from the disease. We present a simple method, employing external data from previously published randomized controlled trials of screening, of correction for this bias. We illustrate it by using data from a case-control study performed within the invited arm of the Malmo mammographic screening trial, a prospective study from the service screening programme in two counties in Sweden, and a matched case-control study of mammographic screening in Florence, Italy.
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- Tabar, L, et al.
(författare)
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Beyond randomized controlled trials - Organized mammographic screening substantially reduces breast carcinoma mortality
- 2001
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Ingår i: Cancer. - 0008-543X .- 1097-0142. ; 91:9, s. 1724-1731
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND, The efficacy of mammographic screening in the reduction of breast carcinoma mortality has been demonstrated in randomized controlled trials. However, the evaluation of organized screening outside of research settings (so-called "service screening") faces unique methodologic and conceptual challenges. The current study describes the evaluation of organized mammography screening in a clinical setting and demonstrates the benefit obtained from service screening in two Swedish counties. METHODS. In the group of subjects ages 20-69 years, there were 6807 women diagnosed with breast carcinoma over a 29-year period in 2 counties in Sweden and 1863 breast carcinoma deaths. All patients were classified from patient charts based on their screening status (i.e., whether they had been invited to undergo screening and whether they actually had undergone screening). The number of women who lived in the 2 counties during the 29-year study period was provided by the Central Bureau of Statistics. Breast carcinoma-specific mortality was compared across three time periods: 1) 1968-1977, when no screening was taking place because mammography had not been introduced, 2) 1978-1987, the approximate period of the Two-County randomized controlled trial of screening in women ages 40-74 years, and 3) 1988-1996, when all women in the 2 counties ages 40-69 years were invited to undergo screening (service screening). When comparing breast carcinoma mortality in screened women with that in women diagnosed before screening was introduced, a correction for self-selection bias was incorporated to prevent overestimation of the benefit of screening. RESULTS. The mortality from incident breast carcinoma diagnosed in women ages 40-69 years who actually were screened during the service screening period (1988-1996) declined significantly by 63% (relative risk [RR] = 0.37, 95% CI, 0.30-0.46) compared with breast carcinoma mortality during the time period when no screening was available (1968-1977). The mortality decline was 50% (RR = 0.50, 95% CI, 0.41-0.60) when breast carcinoma mortality among all women who were invited to undergo screening (nonattendees included) was compared with breast cancer mortality during the time period when no screening was available (1968-1977). The reduction in mortality observed during the service screening period, adjusted for selection bias, was 48% (RR = 0.52, 95% CI, 0.43-0.63). No significant change in breast carcinoma mortality was observed over the three time periods in women who did not undergo screening. This group included women ages 20-39 years because these individuals were never invited to undergo screening, and women ages 40-69 years who did not undergo screening (not invited during the randomized trial or invited during the second and third time periods but declined). CONCLUSIONS. Regular mammographic screening resulted in a 63% reduction in breast carcinoma death among women who actually underwent screening. The policy of invitation to organized screening with mammography appears to have reduced breast carcinoma mortality by 50% in these 2 counties. (C) 2001 American Cancer Society.
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- Tabar, L, et al.
(författare)
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Mammography service screening and mortality in breast cancer patients : 20-year follow-up before and after introduction of screening
- 2003
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Ingår i: The Lancet. - 0140-6736 .- 1474-547X. ; 361:9367, s. 1405-1410
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Tidskriftsartikel (refereegranskat)abstract
- Background: The long term effect of mammographic service screening is not well established. We aimed to assess the long-term effect of mammographic screening on death from breast cancer, taking into account potential biases from self-selection, changes in breast cancer incidence, and classification of cause of death. Methods: We compared deaths from breast cancer diagnosed in the 20 years before screening was introduced (1958-77) with those from breast cancer diagnosed in the 20 years after the introduction of screening (1978-97) in two Swedish counties, in 210 000 women aged 20-69 years. We also compared deaths from all cancers and from all causes in patients diagnosed with breast cancer in the 20 years before and after screening was introduced. In the analysis, data were stratified into age-groups invited for screening (40-69 years) and not invited (20-39 years), and by whether or not the women had actually received screening. We also analysed mortality for the 40-49-year age-group separately. Findings: The unadjusted risk of death from breast cancer dropped significantly in the second screening period compared with the first in women aged 40-69 years (relative risk [RR] 0.77 [95% CI 0.7-0.85], p<0.0001). No such decline was seen in 20-39 year olds. After adjustment for age, self-selection bias, and changes in breast-cancer incidence in the 40-69 years age-group, breast-cancer mortality was reduced in women who were screened (0.56, 0.49-0.64 p<0.0001), in those who were not screened (0.84 [0.71-0.99], p=0.03), and in screened and unscreened women combined (0.59 [0.53-0.66], p<0.0001). After adjustment for age, self-selection bias, and changes in incidence in the 40-49-year age-group, deaths from breast cancer fell significantly in those who were screened (0.52 [0.4-0.67], p<0.0001), and in all women, screened and unscreened combined (0.55 [0.44-0.7] p<0.0001) but not in unscreened women (p=0.2). In both 40-69-year and 40-49-year age-groups, reductions in deaths from all cancers and from all-causes in women with breast cancer were consistent with these results. Interpretation Taking account of potential biases, changes in clinical practice and changes in the incidence of breast cancer, mammography screening is contributing to substantial reductions in breast cancer mortality in these two Swedish counties.
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- Tabar, L, et al.
(författare)
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The Swedish two-county trial twenty years later - Updated mortality results and new insights from long-term follow-up
- 2000
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Ingår i: The Radiologic clinics of North America. - 0033-8389 .- 1557-8275. ; 38:4, s. 625-
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Tidskriftsartikel (refereegranskat)abstract
- This article updates the results 20 years later of the Swedish Two-County Trial of mammographic screening for breast cancer. The result remains a substantial and significant 32% reduction in breast cancer mortality in association with an invitation to be screened. It is shown that the effect of screening can be ascribed to a shift in the prognostic character of the tumors diagnosed, that in turn can be used as a measure of the quality of a screening program. The results on prognosis also identify a group of small but high-risk tumors, with fundamental implications for diagnosis and treatment.
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