Observed and Predicted Risk of Breast Cancer Death in Randomized Trials on Breast Cancer Screening.
The role of breast screening in breast cancer mortality declines is debated. Screening impacts cancer mortality through decreasing the number of advanced cancers with poor diagnosis, while cancer treatment works through decreasing the case-fatality rate. Hence, reductions in cancer death rates thanks to screening should directly reflect reductions in advanced cancer rates. We verified whether in breast screening trials, the observed reductions in the risk of breast cancer death could be predicted from reductions of advanced breast cancer rates.



The Greater New York Health Insurance Plan trial (HIP) is the only breast screening trial that reported stage-specific cancer fatality for the screening and for the control group separately. The Swedish Two-County trial (TCT)) reported size-specific fatalities for cancer patients in both screening and control groups. We computed predicted numbers of breast cancer deaths, from which we calculated predicted relative risks (RR) and (95% confidence intervals). The Age trial in England performed its own calculations of predicted relative risk.



The observed and predicted RR of breast cancer death were 0.72 (0.56-0.94) and 0.98 (0.77-1.24) in the HIP trial, and 0.79 (0.78-1.01) and 0.90 (0.80-1.01) in the Age trial. In the TCT, the observed RR was 0.73 (0.62-0.87), while the predicted RR was 0.89 (0.75-1.05) if overdiagnosis was assumed to be negligible and 0.83 (0.70-0.97) if extra cancers were excluded.



In breast screening trials, factors other than screening have contributed to reductions in the risk of breast cancer death most probably by reducing the fatality of advanced cancers in screening groups. These factors were the better management of breast cancer patients and the underreporting of breast cancer as the underlying cause of death. Breast screening trials should publish stage-specific fatalities observed in each group.
Strathclyde Institute of Global Public Health at iPRI, Lyon, France.|International Prevention Research Institute (iPRI), Lyon, France.
Philippe
P
Autier
Strathclyde Institute of Global Public Health at iPRI, Lyon, France.|International Prevention Research Institute (iPRI), Lyon, France.
Mathieu
0000-0003-1052-5604
M
Boniol
International Prevention Research Institute (iPRI), Lyon, France.
Michel
0000-0003-2476-4868
M
Smans
Institute of Cancer Policy, Kings Health Partners Cancer Centre, Bermondsey Wing, Guy's Campus, London, United Kingdom.
Richard
R
Sullivan
Strathclyde Institute of Global Public Health at iPRI, Lyon, France.|International Prevention Research Institute (iPRI), Lyon, France.
Peter
P
Boyle
D001943:Breast Neoplasms / Q000175:diagnosis* / Q000401:mortality; D055088:Early Detection of Cancer / Q000379:methods* / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D008403:Mass Screening / Q000379:methods* / Q000706:statistics & numerical data; D016032:Randomized Controlled Trials as Topic; D018570:Risk Assessment / Q000379:methods / Q000706:statistics & numerical data; D012307:Risk Factors; D016019:Survival Analysis; D015996:Survival Rate