In Norway, all women aged 50-69 have been invited for biennial breast cancer screening since the Norwegian Breast Cancer Screening Program went national in 2004. This month, the Research Council of Norway submitted its findings on the effectiveness of the program, finding that it has largely met expectations.

An evaluation report submitted to Norway’s Minister of Health and Care Services Bent Høie showed the program cut breast cancer mortality rates by 20 to 30 percent among women who were followed until age 79. This nears the primary target of 30 percent, according to Roar Johnsen, MD, PhD, of the Norwegian University of Science and Technology, who chaired the evaluation steering committee.

On the flipside, researchers found that the probability of being overdiagnosed by screening is greater than five times the probability of avoiding death by breast cancer. For every 10,000 women invited to 10 rounds of screening, approximately 377 tumors or premalignant lesions will be detected, with around 27 women from this group avoiding death thanks to early detection. Approximately 142 patients will be overdiagnosed and potentially face anxiety and unnecessary treatment for a disease that would not harm them in their lifetime.

"There is a large degree of uncertainty with these figures," said Johnsen in a press release. "Each woman must weigh the advantages and disadvantages of her own situation when deciding whether to accept the offer of free screening."

The Norwegian Breast Cancer Screening Program began on a smaller scale in the mid-1990s, gradually growing in the number of counties it included. This stepwise inclusion enabled comparison between those who were invited to be screened and those who weren’t yet exposed to the program. The Research Council of Norway invited researchers from around the country and around the world to analyze the data, tackling the issue of benefits and harms from different angles, and ultimately accepted seven applications for studies that, taken together, offered a picture of the screening program’s effectiveness.

Other findings in the report included estimates of costs, which showed the screening program cost NOK 1,389 ($179 USD) per woman attending screening in 2012, including costs of the screening exam, recall exam and indirect costs.

Attendance per screening round was 76 percent, with 83 percent of invited women attending at least one examination. Among those who attended 10 screening invitations, about one-in-five were recalled at least once for a false positive result.

Across Norway, there were approximately 660 deaths from breast cancer per year in the 1990s among women age 50 and older, though that number had dropped to 588 deaths in 2012. Roughly two-thirds of all breast cancers among those aged 50-69 in the country are diagnosed through the national screening program.

“The estimates indicate that the Norwegian program performs on average at the level that could be expected from the majority of previous reviews of the mammography screening trials,” read the report. “From a societal perspective, recognizing the uncertainty of the estimates, the cost-effectiveness of the program seems to be within the range of what Norwegian Health Authorities define as acceptable for health services. On the individual level, however, each invited woman has to weigh the information on potential benefits and harms based on her own values, health and life situation when deciding on whether or not to attend the program.”