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.

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.

Study 1

Inclusion Criteria:

• Breast cancer diagnosed within BreastScreen Norway using digital mammography
• Prior screening images available for review

Study 2

Inclusion Criteria:

• Women born between 1927 and 1934 (inclusive)
• Legal resident in Norway at any time between 1996 and 2003 (inclusive)

Study 3

Inclusion Criteria:

• Women residing in Norway, aged 50-69 (inclusive)
• Practising family doctors in Norway, aged 25-75 (inclusive)
• Provide informed consent

Women aged 50-69, and practising female and male family doctors aged 25-75, residing in Norway.