Overdiagnosis and “underdiagnosis” in BreastScreen Norway

Abstract

One in eleven women in Norway will be diagnosed with breast cancer by age 75. Organized mammographic screening can detect early stage breast cancer and reduce deaths from this disease. However, screening involves harms, such as the potential detection of a slow growing breast cancer that would never present symptomatically during a woman’s lifetime (overdiagnosis). “Underdiagnosis” can also occur, which was defined as “failing” to diagnose a breast cancer that would present symptomatically during a woman’s lifetime. This thesis aimed to generate knowledge about these harms through three studies. The first study demonstrated that radiologists and pathologists preferentially round tumour diameter measurements, which can lead to understaging but not overstaging. The second study considered whether women with “missed” cancers that were diagnosed at a subsequent screening examination could be underdiagnosed. Based on their tumour characteristics and survival profile, it was posited that these women received a timely diagnosis. The last study indicated that women have relatively less knowledge about overdiagnosis than other topics related to mammographic screening. This study highlights some of the challenges related to communicating information about overdiagnosis and screening.