Purpose: Mammography screening has been found to reduce breast cancer mortality, but is also accompanied by harms, such as overdiagnosis. Overdiagnosis refers to the detection of tumors that would not have been detected in a woman’s lifetime in the absence of screening. Estimates of the amount of overdiagnosis vary widely. The aim of the present study is to estimate the amount of overdiagnosis for invasive breast cancer and ductal carcinoma in situ associated with screening women after age 74 years.
Method: The microsimulation model MISCAN-Fadia was used to simulate a cohort of women born in 1960. All women received biennial screening starting at age 50 with varying stopping ages of screening. First, we simulated the screening currently recommended, i.e., biennial screening from age 50 to 74 years, and determined the benefits and harms of the last screen at age 74 years. Then, the additional benefits and harms of adding one screen were estimated with increasing stopping ages. We estimated the number of life years gained, quality-adjusted life years, breast cancer deaths averted, false positives and number of overdiagnosed women for each screening scenario.
Result: The model predicted that screening after age 74 years resulted in benefits in terms of breast cancer deaths averted and life years gained with no upper age limit. The number of quality-adjusted life-years gained increased for screening up to age 90 years. The number of overdiagnosed women increased steeply with increasing upper age of screening. For screening women between age 50 and 74 years 4% of the invasive breast cancers that were detected were overdiagnosed, increasing to 13% for a screen at age 80 years, and 30% for a screen at age 90 years.
Conclusion: Screening women after age 74 years results in a less favorable balance of benefits and harms than screening women between the ages of 50 and 74 years, because of the increasing amount of overdiagnosis at older ages. Decisions on the appropriate upper age depend on individual preferences. Estimates of overdiagnosis are crucial to inform women about the balance of benefits and harms of mammography screening at higher ages.