Introduction
Breast cancer is the most common cancer in women, both in terms of new cases and mortality. The incidence is still increasing. Most of the known risk factors are difficult to address through primary prevention measures, which makes secondary prevention measures, especially screening, all the more important. In 2003, the Council of the EU issued recommendations for the introduction of evidence-based organized cancer screening programmes, including for breast cancer, which were updated in 2022. In 2008, Slovenia started with organized mammography screening for women aged 50–69 every two years. Slovenian Breast Cancer Screening Programme DORA was gradually expanded to cover the entire country by 2018.
In this work, we aimed to evaluate the benefits of the introduction of organized screening for breast cancer in the Slovenian population and assess the consequences of the step-wise introduction of the screening programme.
Methods
In the cohort study, incidence data on breast cancer cases from population-based Slovenian Cancer Registry in the period 1998–2018 was used. For the period 2008–2018 we used also the data on enrollment in the screening programme obtained from the screening registry of the DORA programme. In the target age group of 50–69 years, incidence trends were analyzed, comparing stage at diagnosis, age at diagnosis, first treatment modalities and time from diagnosis to first treatment stratified according to screening programme enrollment status. We also included socio-economic status as an explanatory variable in the regression models.
To study mortality, we used data on breast cancer deaths in the period 1998–2019 from the Slovenian Cancer Registry, which we supplemented with data on the roll-out of the DORA programme across municipalities. We examined and compared temporal trends in mortality and the absolute and relative differences before, during and after the introduction of the screening programme between different areas according to the expansion of the DORA programme. We also analyzed net survival by stage and calculated years of life gained during the roll-out period as a result of the introduction of population screening.
Results
In the 50–69 age group, the time trend analysis of incidence shows an increase in the localized stage of breast cancer, a decline in the regional stage of disease after 2008, following a previous increase, and a downward trend in the distant stage. Women included in the DORA programme have a lower stage at diagnosis and are around two years younger. The mean time to surgery was shorter for women outside the DORA programme, but shows high variability, possibly due to the absence of established treatment processes that ensure higher quality of care in organized screenings. This is also reflected in the calculation of survival, where at all stages, women enrolled in the DORA programme have significantly better survival than those not enrolled in the programme or non-responders.
The mortality trend shows a decline throughout the entire period. Comparison of mortality during the roll-out period between municipalities with and without the DORA programme shows no differences between the two groups, most likely due to the follow-up time being too short. The mortality rate after the full roll-out of organized screening is 17.5% lower (95% confidence interval 3.6–29.5) than before the introduction of the programme. This fall can not be directly attributed to introduction of organized screening; thus, it is moving in the expected direction. Trends in mortality should be observed also in the future. The introduction of screening has saved 90.6 years of life by 2018, and if the DORA programme had been implemented nationwide in 2008, it would have saved 552.7 years (95% confidence interval 106.4–999.0).
Conclusions
The results regarding the stage and age at diagnosis are expected and indicate the medium-term effectiveness of the organized screening programme. We expect that positive results will be even more pronounced in the future, now that organized screening has been fully implemented. Despite the fact that the time from diagnosis to surgery was slightly longer in the DORA programme, survival outcomes were better for women enrolled in the DORA programme, which suggests that the quality of treatment is more important than the speed.
Despite limitations and possible biases, results of this research point to the benefits of organized screening for breast cancer in the population. Any changes in screening should be introduced in the shortest possible period across the entire area, as this will ensure the greatest benefit without causing temporary systemic inequalities.
|
