Women’s conceptual knowledge about breast cancer screening and overdiagnosis in Norway: a cross-sectional study

OBJECTIVE: To investigate conceptual knowledge about mammographic screening among Norwegian women. DESIGN: We administered a cross-sectional, web-based survey. We used multiple-choice questions and a grading rubric published by a research group from Australia. SETTING: Our Norwegian-language survey was open from April to June 2020 and targeted women aged 45–74 years. PARTICIPANTS: 2033 women completed our questionnaire. We excluded 13 women outside the target age range and 128 women with incomplete data. Responses from 1892 women were included in the final study sample. PRIMARY AND SECONDARY OUTCOME MEASURES: The questionnaire focused on women’s knowledge about the breast cancer mortality reduction, false positive results and overdiagnosis associated with mammographic screening. The primary outcome was the mean number of marks assigned in each of the three themes and overall. There were three potential marks for questions about breast cancer mortality, one for false positives and six for overdiagnosis. RESULTS: Most women (91.7%) correctly reported that screened women are less likely to die of breast cancer than non-screened women. 39.7% of women reported having heard of a ‘false positive screening result’ and 86.2% identified the term’s definition; 51.3% of women had heard of ‘overdiagnosis’ and 14.8% identified the term’s definition. The mean score was 2.59 of 3 for questions about breast cancer mortality benefit and 0.93 of 1 for the question about false positive screening results. It was 2.23 of 6 for questions about overdiagnosis. CONCLUSIONS: Most participants correctly answered questions about the breast cancer mortality benefit and false positive results associated with screening. The proportion of correct responses to questions about overdiagnosis was modest, indicating that conceptual knowledge about overdiagnosis was lower. Qualitative studies that can obtain in-depth information about women’s understanding of overdiagnosis may help improve Norwegian-language information about this challenging topic.