A decline in breast cancer mortality has been observed in western European Countries since the middle of the 1990s.

Different methodological approaches, including case-control studies, incidence-based mortality studies, and trend studies, have been used to assess the effectiveness of mammography screening programmes in reducing breast cancer mortality. However, not all methods succeed in distinguishing the relative contributions of service screening and taking correctly into consideration the potential source of bias that might affect the estimate.

Recently, a review of six case-control studies confirmed a breast cancer mortality reduction ranging from 38% to 70% among screened women. This figure is in accordance with the estimate obtained from incidence-based mortality studies if screening compliance is taken into account. We will describe the methodological constraints of mortality trend studies in predicting the impact of screening on mortality and the necessary caution that must be applied when interpreting the results of such studies.

In conclusion, when appropriate methodological approaches are used, it is evident that mammographic screening programmes have contributed substantially to the observed decline in breast cancer mortality.

Introduction

The use of screening mammography is still under debate within the medical community. The aim of this study is to define a balance sheet of benefits (breast cancer mortality reduction) and harms (overdiagnosis) for mammography screening programs.

Methods

We compared breast cancer incidence and mortality in two cohorts of women, defined as 'attenders' or 'non-attenders' on the basis of the individual attitudes towards screening, who were invited to the first round of the Florentine screening program. The effects of screening exposure on breast cancer incidence and mortality were evaluated by fitting Poisson regression models adjusted for age at entry, marital status and deprivation index. We performed a sensitivity analysis excluding 34 women not responding to the invitation with a breast cancer diagnosis in the following six months.

Results

In total, we included 51,096 women aged 50 to 69 years invited at the first screening round (1991 to 1993) and followed-up for breast cancer incidence and mortality until 31 December 2007 and 31 December 2008, respectively The estimate of mortality reduction varies from 45% among 50 to 59 year-old women up to 51% among 60 to 69 year-old women. The estimate of overdiagnosis, according to the cumulative-incidence method, is an additional 10% of all breast cancer cases among 60 to 69 year-old women screened.

Conclusions

Comparing the breast cancer mortality and breast cancer incidence between attenders and non-attenders, we have determined that the overall cost to save one life corresponds to no more than one over-diagnosed tumor (from 0.6 to 1 depending on the selection criteria of the cohort), even if a residual self-selection bias cannot be excluded.

Introduction

Excess of incidence rates is the expected consequence of service screening. The aim of this paper is to estimate the quota attributable to overdiagnosis in the breast cancer screening programmes in Northern and Central Italy.

Methods

All patients with breast cancer diagnosed between 50 and 74 years who were resident in screening areas in the six years before and five years after the start of the screening programme were included. We calculated a corrected-for-lead-time number of observed cases for each calendar year. The number of observed incident cases was reduced by the number of screen-detected cases in that year and incremented by the estimated number of screen-detected cases that would have arisen clinically in that year.

Results

In total we included 13,519 and 13,999 breast cancer cases diagnosed in the pre-screening and screening years, respectively. In total, the excess ratio of observed to predicted in situ and invasive cases was 36.2%. After correction for lead time the excess ratio was 4.6% (95% confidence interval 2 to 7%) and for invasive cases only it was 3.2% (95% confidence interval 1 to 6%).

Conclusion

The remaining excess of cancers after individual correction for lead time was lower than 5%.