Nearly 1 in 5 women who receive the recommended 10 biennial screening rounds for breast cancer in Norway will get a false positive result, and 1 in 20 women will receive a false positive result that leads to an invasive procedure, a new analysis shows.
While the risk may seem high, it is actually much lower than what researchers have reported in the U.S., the study authors note in their paper, published online Dec. 21 in Cancer.
“I am proud about the low rate of recalls we have in Norway and Europe – and hope we can keep it that low for the future,” said senior author Solveig Hofvind, PhD, head of BreastScreen Norway, a nationwide screening program that invites women aged 50 to 69 to mammographic screening every other year.
“The double reading in Europe is probably the main reason for the lower rate in Europe compared to the U.S., where single reading is used,” she said in an interview.
Until now, Dr. Hofvind and her colleagues say, no studies have been performed using exclusively empirical data to describe the cumulative risk of experiencing a false positive screening result in Europe because of the need for long-term follow-up and complete data registration.
For their study, the researchers turned to the Cancer Registry of Norway, which administers BreastScreen Norway. They focused on data from 1995 to 2019 on women aged 50 to 69 years who had attended one or more screening rounds and could potentially attend all 10 screening examinations over the 20-year period.
Women were excluded if they were diagnosed with breast cancer before attending screening, participated in interventional research, self-referred for screening, were recalled due to self-reported symptoms or technically inadequate mammograms, or declined follow-up after a positive screen.
Among more than 421,000 women who underwent nearly 1.9 million screening examinations, 11.3% experienced at least one false positive result and 3.3% experienced at least one false positive involving an invasive procedure, such as fine-needle aspiration cytology, core-needle biopsy, or open biopsy.
The cumulative risk of experiencing a first false positive screen was 18.0% and that of experiencing a false positive that involved an invasive procedure was 5.01%. Adjusting for irregular attendance, age at screening, or the number of screens attended had little effect on the estimates.
The results closely match earlier findings from Norway that have been based on assumptions rather than exclusively empirical data. However, these findings differ from results reported in U.S. studies, which have relied largely on data from the Breast Cancer Surveillance Consortium, the researchers say.
“The latter have indicated that, for women who initiate biennial screening at the age of 50 years, the cumulative risk after 10 years is 42% for experiencing at least one false-positive screening result and 6.4% for experiencing at least one false-positive screening result involving an invasive procedure,” Dr. Hofvind and her colleagues write.
Several principal investigators with the Breast Cancer Surveillance Consortium did not respond or were unavailable for comment when contacted by this news organization.
However, the study authors highlighted several factors that could help explain the discrepancy between the U.S. and European results.
In addition to double mammogram reading, “European guidelines recommend that breast radiologists read 3,500 to 11,000 mammograms annually, whereas 960 every 2 years are required by the U.S. Mammography Quality Standards Act,” the researchers note. They also point out that previous screening mammograms are readily available in Norway, whereas this is not always the case in the U.S.
“False-positive screening results are a part of the screening for breast cancer – and the women need to be informed about the risk,” Dr. Hofvind concluded. “The screening programs should aim to keep the rate as low as possible for the women [given] the costs.”
The study was supported by the Dam Foundation via the Norwegian Breast Cancer Society.
A version of this article first appeared on Medscape.com.