Rate of over-diagnosis of breast cancer 15 years after end of Malmo mammographic screening trial: follow-up study

Objective To evaluate the rate of over-diagnosis of breast cancer 15 years after the end of the Malmo mammographic screening trial. Design Follow-up Study. Setting Malmo, Sweden. Subjects 42 283 women aged 45-69 years at randomisation. Interventions Screening for breast cancer with mammography or not (controls). Screening was offered at end of randomisation design to both groups aged 45-54 at randomisation but not to groups aged 55-69 at randomisation. Main outcome measures Rate of over-diagnosis of breast cancer (in situ and invasive), calculated as incidence in the invited and control groups, during period of randomised design (period 1), during period randomised design ended (period 2), and at end of follow-up. Results In women aged 55-69 years at randomisation the relative rates of over-diagnosis of breast cancer (95% confidence intervals) were 1.32 (1.14 to 1.53) for period 1, 0.92 (0.79 to 1.06) for period 2, and 1.10 (0.99 to 1.22) at the end of follow-up. Conclusion Conclusions on over-diagnosis of breast cancer in the Malmo mammographic screening trial can be drawn mainly in women aged 55-69 years at randomisation whose control groups were never screened. Fifteen years after die trial ended the rate of over-diagnosis of breast cancer was 10% in this age group.