Elsevier

The Lancet Oncology

Volume 4, Issue 4, April 2003, Pages 251-254
The Lancet Oncology

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Why is breast-cancer mortality declining?

https://doi.org/10.1016/S1470-2045(03)01037-4Get rights and content

Summary

Population statistics indicate that age-adjusted breast-cancer mortality rates began to decline during the early 1990s in many developed countries. For several decades before 1990, breast-cancer mortality rates in these countries had been either stable or increasing. Many investigators attribute the decline in mortality to mammography screening. However, randomised prospective trials indicate that there is a delay of 10 years before the effect of such screening can be seen in mortality statistics. In many developed countries, screening programmes were launched in the late 1980s and early 1990s, so the sudden decline in breast-cancer mortality in the early 1990s was much too soon to be attributable to mammography screening. In this review, we argue that although some of the decline in breast-cancer mortality is due to a reduction in breast-cancer risk, most of it can probably be attributed to adjuvant systemic therapy and the earlier detection of palpable tumours. We also explain why advances in the treatment of breast cancer might be outpacing the value of mammography screening. Since age-adjusted mortality rates are the most basic measure of progress in the treatment of breast cancer, we suggest that careful scrutiny of recent trends in breast-cancer mortality may provide important insights into the effectiveness of novel strategies for diagnosis and treatment.

Section snippets

Reduction in risk

Mammography screening allows much earlier detection and diagnosis of breast cancer, but also detects some non-progressive cancers. Thus, the incidence of breast cancer artificially increased after the introduction of mammography screening programmes in the late 1980s. However, this increase in incidence was less than expected, which suggested that there was also a decline in the inherent risk of developing the disease.4 The recent decline in mortality might, therefore, be partly explained by a

Mammography screening

Eight randomised prospective trials have examined the effect of mammography screening on breast-cancer mortality.9 Overviews of these trials have shown that a relation between reduction in breast-cancer mortality and mammography screening takes 7–10 years to emerge. Patients with cancers that were detected before screening began were excluded from the studies. However, in population statistics, the cancers detected before the introduction of screening are not excluded from the total number of

The role of therapy

In the 1980s, there were substantial advances in the treatment of breast cancer. The results of several large randomised trials indicated that adjuvant systemic therapy could decrease breast-cancer mortality by about 20%.17 This benefit emerged about 3 years after these trials had begun. By the late 1980s, tamoxifen and polychemotherapy were widely prescribed in many developed countries as adjuvant therapy after surgery for primary breast cancer. Any favourable effect of adjuvant systemic

Earlier detection of palpable cancers

In the 1980s, there was a heightened awareness of breast cancer by both physicians and the public, and the number of patients with small, palpable tumours referred for treatment increased. We suggest that the earlier detection of palpable cancers has had a significant role in the decline in breast-cancer mortality.

Indeed, we could speculate that the entire benefit of breast-cancer screening is attributable to the earlier detection of palpable cancers, with detection of impalpable cancers

Conclusion

Olsen and Gøtzsche reported imbalances between control and study groups in several of the mammography screening trials and questioned the validity of their results.22 In their assessment, only the CNBSS trial was without bias. Thus, careful scrutiny of the age-adjusted breast-cancer mortality statistics is extremely relevant in elucidating the potential effect of mammography screening. Age-adjusted mortality rates are the most basic measure of progress against cancer. If novel strategies in the

Search strategy and selection criteria

Papers for this review were identified by searches of PubMed with the terms “breast cancer”, “mortality”, “population statistics”, and “decline”. References from between 1980 and 2002 were selected. Additional papers were identified from the reference lists of some articles. No language restrictions were applied.

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  • Cited by (194)

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