Mammographic screening among women aged 50-69 reduces breast cancer mortality but also carries some risk. This PhD project will study under- and overdiagnosis, two risks associated with mammographic screening, in BreastScreen Norway. Underdiagnosis can occur when a tumour is present but not detected as a result of screening, while overdiagnosis can occur when a woman is diagnosed with a slow growing cancer that would not become symptomatic during her lifetime.~This project will address the following topics and research questions using observational study methods.~Study 1: To determine whether tumour histopathology and survival differentially associated with potentially under- or overdiagnosed interval and screen-detected breast cancers.~Do women with potentially underdiagnosed interval cancers have different tumour histopathology and survival than those whose interval cancers showed no signs at the prior screen?~Do women with potentially overdiagnosed screen-detected cancer have different tumour histopathology and survival than those whose screen-detected cancer showed no signs at the prior screen?~Study 2: To estimate overdiagnosis in the screening program using individual-level data:~What was the rate of overdiagnosis for women screened in the program during 1996-2003?~How does adjusting for sociodemographic factors affect estimates of overdiagnosis?~Study 3: To describe awareness and knowledge about under- and overdiagnosis and breast screening in general:~Are women aware of and knowledgeable about under- and overdiagnosis in breast screening?~Are family doctors aware of and knowledgeable about breast screening, and under- and overdiagnosis? Are they confident in their ability to relay this information to their patients?~Study 1 is a quality improvement study and has approval from Personvernombudet (PVO 2016-4696). Study 2 has research ethics board (REK) approval (REK 2013/795), while REK approval will be sought for Study 3.
This PhD project will describe tumour characteristics and survival associated with of under- and overdiagnosed breast cancers, the rate of overdiagnosis in BreastScreen Norway, and whether women and family doctors are aware of, and knowledgeable about, under- and overdiagnosis in breast cancer screening.