Abstract
BackgroundThe 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.Patients and MethodsThe 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.ResultsThe 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.ConclusionsIn 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.
Highlights
IntroductionIn 1985, publications of the Greater New-York Health Insurance Plan and of the Two-County Trial suggested that 2 to 4 rounds of breast screening could reduce the risk of breast cancer death by 30% [1, 2]
Breast screening trials should publish stage-specific fatalities observed in each group
In 1985, publications of the Greater New-York Health Insurance Plan and of the Two-County Trial suggested that 2 to 4 rounds of breast screening could reduce the risk of breast cancer death by 30% [1, 2]
Summary
In 1985, publications of the Greater New-York Health Insurance Plan and of the Two-County Trial suggested that 2 to 4 rounds of breast screening could reduce the risk of breast cancer death by 30% [1, 2]. No association was found between the timing and magnitude of declining trends in breast cancer mortality and the timing of mammography screening implementation in the various States of the USA [12]. This apparent absence of impact of mammography screening on breast cancer mortality was in sharp contrast with studies that clearly showed quicker and steeper reductions in the risk of cervical and colorectal cancers in areas where screening is widespread, compared to areas where screening is not common [13,14,15]. 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
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