Evaluation issues in the Swedish Two-County Trial of breast cancer screening: An historical review.
Objectives To summarize debate and research in the Swedish Two-County Trial of mammographic screening on key issues of trial design, endpoint evaluation, and overdiagnosis, and from these to infer promising directions for the future. Methods A cluster-randomized controlled trial of the offer of breast cancer screening in Sweden, with a single screen of the control group at the end of the screening phase forms the setting for a historical review of investigations and debate on issues of design, analysis, and interpretation of results of the trial. Results There has been considerable commentary on the closure screen of the control group, ascertainment of cause of death, and cluster randomization. The issues raised were researched in detail and the main questions answered in publications between 1989 and 2003. Overdiagnosis issues still remain, but methods of estimation taking full account of lead time and of non-screening influences on incidence (taking place mainly before 2005) suggest that it is a minor phenomenon. Conclusion Despite resolution of issues relating to this trial in peer-reviewed publications dating from years, or even decades ago, issues that already have been addressed continue to be raised. We suggest that it would be more profitable to concentrate efforts on current research issues in breast cancer diagnosis, treatment, and prevention.
1 University of Uppsala, Uppsala, Sweden.
Laszlo
L
Tabar
2 National Taiwan University, Taipei, Taiwan.
Tony Hsiu-Hsi
TH
Chen
2 National Taiwan University, Taipei, Taiwan.
Chen-Yang
CY
Hsu
2 National Taiwan University, Taipei, Taiwan.
Wendy Yi-Ying
WY
Wu
3 Taipei Medical University, Taipei, Taiwan.
Amy Ming-Fang
AM
Yen
3 Taipei Medical University, Taipei, Taiwan.
Sam Li-Sheng
SL
Chen
4 Chang Gung University, Tao-Yuan, Taiwan.
Sherry Yueh-Hsia
SY
Chiu
5 Kainan University, Tao-Yuan, Taiwan.
Jean Ching-Yuan
JC
Fann
6 University of South Australia, Adelaide, Australia.
Kerri
K
Beckmann
7 American Cancer Society, Atlanta, GA, USA.
Robert A
RA
Smith
8 Queen Mary University of London, London, UK.
Stephen W
SW
Duffy
D000328:Adult; D001943:Breast Neoplasms / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000517:prevention & control; D055088:Early Detection of Cancer / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D015994:Incidence; D008327:Mammography / Q000706:statistics & numerical data*; D008403:Mass Screening / Q000706:statistics & numerical data*; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D016032:Randomized Controlled Trials as Topic; D013548:Sweden / Q000453:epidemiology
Breast cancer screening; mammography; randomised trial