medwireNews: Just under one in five women will experience at least one false–positive result during 10 years of biennial breast screening, population-based data from Norway show.
The study, by Solveig Hofvind (Cancer Registry of Norway, Oslo) and colleagues, included data for 421,545 women who underwent 1,894,523 screening examinations between 1995 and 2019 as part of the BreastScreen Norway program, which targets women aged 50 to 69 years for biennial screening.
The mean age at first attendance was 50.7 years and 4.3% of women attended 10 screening examinations.
During the study period, 10.5% of women received one false-positive screening result and 0.8% had two or more false positives. A false–positive result was defined as recall for further assessment due to abnormal mammographic findings that did not lead to a breast cancer diagnosis within 6 months of screening.
In addition, 3.1% of women had one false–positive result that involved an invasive procedure (fine-needle aspiration cytology, core-needle biopsy, or open biopsy), and 0.1% experienced this on two or more occasions.
Hofvind and team report in Cancer that the false–positive rates were higher during first screens than in subsequent screens, and the cumulative risk for experiencing a first false-positive screening result after 10 rounds of screening was 18.0%. The 10-year cumulative risk was 5.0% for a false–positive result that involved an invasive procedure.
The investigators note that their “empirical approach to calculating the cumulative risk assumed that the risk of experiencing the outcome of interest did not change for women with censored follow-up time.”
This allowed them to include data from as recently as 2019 but meant that follow-up was censored before the women had attended 10 screening rounds in many cases.
In spite of this, the cumulative risk of a first false–positive screening result was 18.3%, and the risk for that including an invasive procedure was 5.1%, after adjustment for the number of screens attended, which the researchers say indicates “that there was minimal bias from dependent censoring.”
Hofvind et al conclude: “As informed choice becomes increasingly important in organized breast cancer screening, it is essential to provide women with accurate information about the cumulative risks associated with attending repeated screening and the increased breast cancer risk associated with false-positive screening results.”
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