Under the Norwegian Breast Cancer Screening Programme, all women aged 50 to 69 are invited for mammography screening every two years. The programme was launched as a pilot project in four counties in 1995/96 and went national in 2004. The purpose of mammography examination is to detect tumours at an early enough stage to begin effective treatment and reduce mortality.The evaluation report was recently submitted to Minister of Health and Care Services Bent Høie.
"The most reliable studies indicate a 20 to 30 per cent reduction in breast cancer mortality in women aged 50 to 69 who have been followed up until the age of 79," says Professor Roar Johnsen of the Norwegian University of Science and Technology (NTNU), who chaired the evaluation steering committee. "This reduction can be said to be close to the primary target of 30 per cent."
Leads to overdiagnosis
The evaluation examined a number of sides to the national screening programme and determined among other things that the probability of being overdiagnosed by screening is five times higher than the probability of avoiding death by breast cancer. Overdiagnosis in this context means that without being screened, the women would never have noticed, been aware of or died from the disease. Under the Norwegian Breast Cancer Screening Programme, all women aged 50 to 69 are invited for mammography screening every two years. Under the programme, for every 10 000 women invited to 10 rounds of screening, roughly 377 cases of tumours or pre-malignant breast lesions will be detected. From this group, roughly 27 women will avoid death from breast cancer as a result of early diagnosis and treatment. However, roughly 142 of them will be overdiagnosed with a disease that will turn out to be harmless.
"There is a large degree of uncertainty with these figures," adds Professor Johnsen. "Each woman must weigh the advantages and disadvantages of her own situation when deciding whether to accept the offer of free screening."
Scientifically sound evaluation
Arvid Hallén, Director General of the Research Council, is very pleased with the evaluation and the steering committee's work.
"This is a good example of what research-based evaluation should be," says Mr Hallén. "The Research Council's role was to find the right researchers for the task. We are very pleased with the way the steering committee and the researchers have conducted the evaluation."
On 7 September the Research Council is organising a national conference, where one of the topics will be the evaluation results.