Long-term cause of death patterns and mode of breast cancer detection in The Netherlands, 2004-2019

Early detection through mammographic screening and various treatment modalities of cancer may have changed life expectancy and cause-specific mortality of breast cancer patients. We aimed to determine the long-term cause of death patterns in screening-detected patients and clinically diagnosed patients in the Netherlands compared with the general population.

Using data from the Netherlands Cancer Registry and Statistics Netherlands of around 26,000 women, aged 50-75 at diagnosis and surgically treated for invasive breast cancer in 2004-2008, we compared patients with screening-detected and clinically diagnosed cancer for major causes of death until 2020. The expected number of all-cause and cause-specific deaths was calculated using rates of the general population.

During the follow-up period, 4310 women died. The age-standardised all-cause mortality ratio for the screening-detected cancer group was 1.41 (95% confidence interval (95% CI), 1.37-1.46). A higher mortality ratio was observed for patients with clinically detected cancer: 2.27 (95% CI, 2.19-2.34). The observed versus expected breast cancer mortality ratio in the screening-detected patient group was 8.92 (95% CI, 8.45-9.40) and 20.23 (19.38-21.09) in the clinical group. Excess mortality was found for lung cancer in both patient groups, and small elevations for circulatory and respiratory disease in the clinically detected group.

Our results indicate that for the screening group no other causes of death but breast and lung cancer were prominent compared with the general population. The clinical group showed excess mortality for some other causes of death as well, suggesting a less healthy group compared with the general population.